these measurements, which the internal evidence shows are untrustworthy, are thrown out, the inversion gives a constant coefficient (see column five), showing t h a t the inversion of cane sugar by acids is of the unimolecular order even in its first stages, as it has aluxys been considered to be. The other similar tables of AIeyer contain the same error, and when the erroneous readings are excluded from them by the above unbiased method, they give satisfactory constancy for the inversion coefficient. i l complete discussion of Meyer‘s results is tleferred to a later article which will present a detailed study t h a t is now in progress of the inversion of cane sugar by invertase and acids. ’fhe present article is only a preliminary communication b u t i t is thought that its immediate publication may be of service to investigators in this field, because the data t h a t are here given are quite sufficient to show. first, t h a t the inversion of cane sugar by acids follows, even in its first stages, the unimolecular order, and second, that the polarimetric measurement (A the in\-ersion of cane sugar by invertase involves a large source of error which can be avoided by adding alkali to the inverting solution before each reading of the polariscope. \\‘hen this source of error is eliminated, as was done by O’Sullivan and ’l‘ompson in their inversion rrieasurernents, the rate follows the unimolecular order. ’The inversion of c m e sugar by invertase is the most thoroughly studied of the numerous enzyme actions; in view of the foregoing proof of its unimolecular ortler may it not be that the other enzyme actions are, after all, quite similar to the usual types of chemical catalysis and t h a t they do not constitute a group t h a t has unique laws of catalytic action, as is now generally I)elievetl? [i‘Cr ITK I U i . T I 01
1: I l 3 - 1:.\c.lorz i \I I L K .
,is11 I'RO'IISISS
I\:
c .\?,E
F3t. Per cetit.
Month.
Xpril . . . . . . . . . >In?.. . . . . . . . . . . June . . . . . . . . . . . July . . . . . . . . . . . August . . . . . . . . . Se1iteiiiI)er. Oc!ol)er
. . . . .? 1 ? . . . . i,,ih . . . . . . ,: ('4 . . . . . . i.0.i . . . . .i . . ,;(I2 -1 2 i
+
Proleini. Per cent.
Casein. P e r cent.
Albuinin. Per cent.
2
X I
2
2')
CL,i2
;,
.iJ2
2
,i4
0
6'
2 1
2
4;
0
;;
,:.
.o; (11
;,
; :\I >
-j.3
1 .4,
I!
I .j
,;
Proteitis. Pc: ct'nt.
Caseiri. I'er cent.
Albumin. Per ceut. , 5.i
1,'
2 .h,
,OO
2
,io
I1
(10
-
,,,> 9 -
(1
,$l
0
\
.' . 2
1'0 1 (>
(II
7
Variations in the Relation of Fat to Proteins in Cow's Milk. We have thus far considered the conditions t h a t affect the percentages of fat and of proteins in milk, without paying attention to the relative variations of these constituents. I t now remains to study the effect of various conditions upon ( I ) the relation of f a t to total proteins, ( 2 ) the relation of fat to casein, and ( 3 ) the relation of casein to albumin. Conditions Affecting the Relation of Fat to Total Proteins and to Casein in Milk. This phase of our subject will be briefly considered under the headings already used in discussing the general subject preceding, and the figures already presented in the foregoing tables will be utilized in furnishing &.&r&&
1I75
F A T A N D PROTEINS I N COW'S MILK.
(a)Breed.-The influence of breed in affecting the relation of fat t o proteins is shown in the following table, the data of which are derived from Table I : TABLEIS.--SHOIVISGI X P L U E N C E O F
RGLATIOSO F F A T
RREED CPOS
T O PROTEISS. Parts of casein for I part of fat.
Parts of proteins for I part of fat.
Fat. Proteins. -.----Per cent, Per cent, Fat : Proteins.
Name of breed,
I. Holstein-Friesian. . ,
3.26
2.84
I
. . . . . . . . 3.76 3. .4merican Holdern 4.01 4,Shorthorn. , . . , , . 4.2s j . Devon . . . . . . . . . . -1 S g 6. Ouernesy.. . . . . . . . . . 5 . 3 s 7 . Jersey.. . . . . .. ,j.i8
3.07 3.32 3.43 3 ,c),3 3 .j6 3.68
I
: 0.87 : 0.82
I
: 0.83
I
: : : :
,
,
,
I I I
0.80
0.80 0.66
0.64
-------
Casein. P e r cent. Fat : Casein. 2.20
I
2.46 2.63 2.79 3 . IO
I
XOI
I
3.03
I
I I I
: 0.67 : 0.65 : 0.66 : 0.65 : 0.63 : 0.54 : o.,i2
It is seen t h a t the different breeds represented separate into two general groups in relation t o the ratio of fat t o total proteins and to casein in milk. I n the case of the first five breeds, the ratio of fat to proteins or to casein does not vary widely. The milk of the Holstein-Friesian breed contains least fat and most proteins in relation to fat. I n the case of the next four breeds in the list, the fat varies from 3 . 7 6 t o 4 . 8 9 per cent. b u t the proteins also vary in very nearly the same ratio as the fat. The Guernsey and Jersey breeds constitute the second group, the fat being high in amount b u t the proteins relatively low. These two breeds vary comparatively little in reference t o the ratio of f a t either to total proteins or to casein. ( b ) Ind,ividuality.--We will notice briefly the variations t h a t occur in case of different individuals of the same breed. The figures in the following table are derived from Table I1 and represent the averages for an entire period of lactation in the case of several different individuals of two breeds. More marked differences could be obtained, of course, by taking single milkings or monthly averages : T A B L E X.-INFLL'ESCE
OF INDIVIDUALITY U P O N
THE RELATIOS O F FATTO PROTEISS.
Parts of proteins for 1 part of f a t .
Iudividual Jerseys.
Fat. Proteins. ----.-Per cent. P e r cent. Fat : Proteins
. . . . . . . . . . . . . . . . . . . j.49
3.57
. . . . . . . . . . . . . . . . . . . j.61 3 . . . . . . . . . . . . . . . . . . . 5.7; 4 . . . . . . . . . . . . . . . . . . . 6.04 j . .. . . . . . . . . . . . . . . . . 6 . 1 j
3.41
I 2
3.69 3.8; 3.96
0.64 I ; 0.64 I ; 0.64 1:o.61 I ; 0.6j
2.9j
I
I
;
Casein. Per cent.
P a r t s of casein for I part of fat.
---
Fat : Casein,.
2.91
I
2.83
I
2.91 3.19 3.43
I
: 0.j6 : 0.53
0.50 ~ : o . j o I : 0.~53
Individual Holstein- Friesians.
I.. ................ 2
...................
3. . . . . . . . . . . . . . . . . . . 5...................
3.0j 3.11 3.16 3,19 3.53
2.60
2.96 2.92
3.34
: 0.97 1 : o . Q 1:0.94 I : 0.91 I : 0.95
;
0.75
2.29
I
2.11
1:0.68 1:o.j6 I : 0.71 I ; 0.77
2.41 2.2j 2.70
I
176
LUCIIjS L. VAN SLYKE.
Whether we take the ratio of f a t to proteins or of fat to casein, there would be very little difficulty in identifying any individual in the list with its proper breed, even though there is some range of variation between the individuals of each breed. (c) Stage of Lactation.---We have previously noticed t h a t during the period of lactation the fat and proteins increase gradually and quite regularly. We will now consider the question as to whether these constituents increase in the same ratio. The data in the following table are derived from the figures given in Table 111.: TABLE SI.--ISP~LUEXC.EOF ST.\(;Eot: I,,KT.\TIOS I:PON PROTEISS.
-------
I....................
.........
4.30
3.16
4.11
2
(,I()
3. . . . . . . . . . . . . . . . . . . 4.21
3.04
4. . . . . . . . . . . . . . . . . . .
4.2j
...................
4.38 4.53 4.j;
3,13 3,25 3.33 3.40 3.4; ,1.5; 3.79 4.04
3
6...................
1.,i()
9 . .. . . . . . . . . . . . . . . . . 4.6; IO..
11
.
FATA S D
Parts o f proteins Parts of casein for 1 part o f f a t . for I part of fat Fat. Proteins. Casein. -----.-Per cent. Per cent. Fat : Proteins. Per cent Fat :Casein.
Month of lactation. 2 . .
T I ~ EKeL.\'rros OF
.
.
..................
+C)O
\j.oj
I : o . ~ + I : 0.73 I
:
0.72
1:0.74 : 0.74 I : 0.74 I 0.74 I : 0.7.; I : o.;G I : o . j i I : o.80
I
~
5
4
I : o . ~ u )
: 0.59 : 0.58 1:0,59
2.42
I
2.46
I
2.52
2.61 2.68 2.74 2.84
I
: 0.60
I
: 0.59 : 0.60
2.90
I
3.01 3.13
I
I I
I
: 0.61 : 0.62 : 0.62 : 0.62
An examination of the fourth and the last columns shows a remarkable uniformity in the ratio of fat to total proteins and to casein throughout most of the period of lactation. During the first three months a very slight tendency appears for the fat to increase with reference to proteins or, stated another way, for the proteins t o decrease in proportion to fat. After this there is very close uniformity up to the eighth month, after which the total proteins increase gradually in relation to fat t o the end of the lactation period. During the last three months of lactation, the fat increases quite rapidly b u t the proteins increase even more rapidly in relation to fat. During this period the casein increases in exact proportion t o fat, maintaining a uniform ratio t h a t is very striking. The close uniformity observed in Table XI is not always so marked, of course, in every individual case, b u t the tendency shown is a very general one. I n this connection we will use the data embodied in Table IV to illustrate the relations under consideration in the case of the mixed milk of many herds of cows, as obtained at cheese-factories. The amount of total proteins shows a tendency to increase relative to f a t for a few months, when a decrease occurs, which is followed by a later increase. The casein maintains a fairly uniform relation to fat during the whole season, except during August, when a decrease was caused
FAT AND PROTEINS IN COW’S MILK.
1177
by the effect of drouth upon pasturage and attendant unfavorable conditions. TABLE ?III.-ISFI,UENCE
O F STAGE O F L.ICTATION C P O S T H E REI,ATIOh’ OF
I’ROTEINS
IiS C.\SE
FATTO
OF CHEESE-FACTORY MILK.
Parts of casein P a r t s of proteins for I part of fat. for I part of fat. Fat. Proteins. Casein. Per cent. P e r cent. F a t : Proteins. Per cent. F a t : Casein.
-----
April.. . . . . . . . . . . . . . .
3.43 3.j8 3.64 3,62
August.. . . . . . . . . . . . . 3.84 3.92 October . . . . . . . . . . . . . . 4 . 2 3
2.81 3.02 3.24 3,0j 3,02 3.20 3.55
I
:
I
: 0.84 : 0.89 : 0.8j : 0.79 0.82 : 0.84
I I I I I
0.82
__--
2.29
I
2.34 2.47 2.43 2.39
I
I
: 0.67 : 0.65 : 0.68 : 0.67 : 0.62
2.55
I
: 0.6j
2.81
I :
I I
0.66
(d) Food and Season.-Attention has previously been called t o the effect of turning cows into pasture, as manifested by changes in the composition of milk in the first and second half of May. We will now notice whether the relation of fat and proteins is changed. Fat. Per cent.
First half of M a y . . . . . SecondhalfofMay . . .
---
P a r t s of proteins P a r t s of casein for I part of fat. f o r I part of fat. Proteins. Casein. P e r cent. Fat : Protein. P e r cent. Fat : Casein.
----
3.46
2.8j
I : 0.82
2.25
I :
3.70
3 . 1 ~
I :
0.86
2.4j
I : 0.66
0.65
It is seen t h a t while the total proteins increased with reference to fat, the ratio of casein t o f a t changed only slightly. (e) Conditions of Milking.-An inspection of Tables V, VI, VI1 and VI11 indicates t h a t the total proteins and the casein also remain fairly uniform while the f a t may vary greatly in the case of milk drawn from the udder in fractional portions, in the case of milk drawn from different quarters of the udder, etc. Conditions Affecting the Relation of Casein to Albumin in Milk. The general statement has peen prominently current in literature to the effect t h a t casein and albumin are present in cow’s milk in very constant relative proportions, the amount of casein being five times that of albumin. Taking herd milks, we have found the casein varying all the way from 2 . 6 t o 5 . 6 parts for one part of albumin. I n single milkings of individual cows, the variations are considerably wider. The data already presented enable us t o study this question under a variety of conditions. ( a ) Breed.-The variation of albumin in relation t o casein in the case of different breeds of cows is shown in the following table, the data of which are derived from Table I. I n studying the results embodied in Table X I I , it is noticeable t h a t the casein and albumin vary more or less in their relative proportions in the case of different breeds of cows, and in no case is the propor-
l'ercent. Perceiit. l'.irts of casein of total o f total proteins proteins i n for I part 61 alhnniiii i n forin of form o f Albnniiii : Caseiii. cnseiri. alhniiiin.
I'roteins. I'er cell 1.
N a m e of breed. Ihlstein-Friesian
7.
Ayrsiiirc . . . . . . . . . ;%Inerican Holderncss
;\
SA
1
:
j
I
1 : 4 i 1
,117
,i; 2 . . . . . . . i 4,; I k v iII1 . . . . . . . . . . . .i0 i (;uer,isey. . . . . . . . . ,; . ,io Jersc!. . . . . . . . . . . . .i. h i
I
Siiclrtiii~rn.
.
1
I
:
_ _ ,, /
22
ir1.1
Il).i]
2 0 ,
~ I ; ~ l liixIic>r l~ i i i rclutioii to iat tlian in mill; with more than 3 iier relit. o!' fat, ivliilc, i i i tlic case of niilk containing more than 4 ,.j 1)cr ccnt. oC i:lt, t l i c s rxtio o!' rxscii! to f:it is less than in milk containin:; Itss t 1 .I .i l)cv w i l t . I ; ; r I . :>t:Lrtiiig i \ , i t i i milk containinK : ~ i i :ivc-ragr o per cciit. or Tat an(i r,i.sc.iii c c ~ i i t c i i t(1: 2 I per cciit., milk with 4 1)
suffice lor this piirpose.
1183
FAT .4XD PROTEIiiS I N C O W ’ S MILK.
The Relation of F a t and Casein in Milk to Yield of Cheese. The two constituents of normal milk which largely determine the yield of cheese are f a t and casein. The exact relation of these two constituents to cheese production have been worked out very carefully a t this station in the case of American cheddar cheese, which is the kind manufactured most extensively in the United States and Canada. Assuming cheese to have the average water content of fresh cheddar cheese, the approximate yield may be easily calculated, if t h e per cent. of f a t in the milk used is known. Thus, t o find the yield of fresh cheese from IOO pounds of milk, multiply the number representing the per cent. of f a t in milk by 2 . 7 . For example, milk containing 3 . 6 per cent. of fat should yield from IOO pounds 9 . 7 2 pounds of green or fresh cheese; with milk containing 3 . 8 per cent. of fat, I O , 26 pounds. This rule applies closely t o normal milk containing 3 . 6 t o 3 . 8 per cent. of fat. For milk containing f a t above 3 . 8 per cent., t h e results are usually too high and for milks containing less than 3 . 6 per cent. of fat, the results are usually low. This is due to the fact t h a t milks low in f a t content usually contain a little more casein in relation t o f a t than do milks high in fat. The yield of cheese can be ascertained more closely when the per cent. of both f a t and casein in milk is known, in the following manner: illultiply the per cent. of casein by 2 . 5 and to this result add the per cent. of fat multiplied by I . I . For approximate results, it is necessary to know only the per cent. of fat, for from this the approximate amount of casein can be calculated by the formula given above. The Relation of F a t and Casein in Milk to Composition and Quality of Cheese. Milk rich in fat, as compared with milk poor in fat, produces cheese containing more fat in proportion t o other constituents. The composition of fresh cheese depends upon the composition of the milk used, provided the process of cheese-making is carried out in a normal manner. The following figures, representing cheese made from Holstein-Friesian milk and from Jersey milk, illustrate this statement clearly. TABLE SSI. - C O A I I , O ~ I T I OF ~ S C I ~ E E ~X\DE E P R O M HOL~TEIS-~~F.!E-X.IY .\XI)i:iio>i J E R C E Y hIILI l . l f I S ~XILI; ; L'I'CS CO.VPO5l'rION
T.\13l.E SSI [.--I
Poll 11d 5
of fat rem o v e d from
poiinds 01 iiiilk.
100
S o r m a l milk anti cliccsc Skim-milk and cheese, . Skirr-xnilk a n d cheese. . . . Skim-milk and cheese. . . .
c) oo
Pounds of fat left i n pounds of tiii:k.
100
1
()(I
I
.oo
,? 00
2
. 5"
I . ,il)
3 . ,io
(' ,j"
Per cent. of fat i n cheese.
.- .
~> I
~>
3 1 .-I 19.0
-, ,, -
P e r cent. of proteins 111 cheese. " 5
021
CHEESE. P a r t s of fat for I part of of proteins. I
Proteins : F a t . I ; 1.65
26.2
I
:
1.20
:7 I
. (1
I
;
0.60
.i 7
'
I
:
0 2 0
(1
The standard adopted by the United States Department of Agriculture depends essentially upon the principle illustrated here, the only difference being t h a t the relation of fat to total solids rather, than to proteins alone, is utilized. Summary. I. Extent o j Data.-The study of the conditions affecting the proportions of fat and proteins in c'ow's milk, as embodied in the preceding article, is based upon the following d a t a : ( I ) 300 analyses of the mixed
FAT AND PROTEINS I N COW’S MILK.
1 1 85
milk of numerous herds, obtained a t cheese-factories, such as is common in the dairy regions of New York State. ( 2 ) 650 analyses of milk of 50 separate herds of cows, covering a period of about six months. (3) Several thousand analyses of milk of individual cows, representing seven different breeds of cows (American Holderness, Ayrshire, Devon, Guernsey] Holstein Friesian, Jersey, Shorthorn) , covering for each individual, several lactation periods and an aggregate of about IOO periods of lactation. 2. Up to 1892 very few determinations of casein proper in cow’s milk had been made in America, the term casein having been wrongly used as synonymous with milk proteins. 3. General Range of Variation in the Percentages of Fat and Proteins in milk,--(^) In single milkings of individual cows, the fat varied from 2 . 2 j to 9.00 per cent. ; the total proteins, from 2.19 to 8 . 5 6 per cent. ; the casein, from 1.59 to 4.49 per cent.; and the albumin, from 0 . 3 1 to 5.32 per cent. The highest percentages are found in case of cows far along in lactation. (2) In the case of individual herds of cows, such as are common in dairy regions of New York State, the fat varied from 2 . 9 0 to 5.50 per cent. ; the total proteins, from 2.31 to 3 . 7 1 per cent. ; the casein, from I . 79 to 3 . 0 2 per cent. ; and the albumin from 0.41 to 0.97 per cent. (3) In the case of milk consisting of a mixture of the milk of many different herds of cows, the f a t varied from 3 . 0 4 to 4.60 per cent. ; total proteins, from 2.53 to 3 . 7 6 per cent. ; casein, from I . 93 to 3.00 per cent.; and albumin, from 0.47 to 0 . 8 8 per cent. 4. Conditions Affecting Variations of Fat and Proteins in Milk.-The following conditions are discussed as those of special prominence in causing variation of percentages of f a t and proteins in milk: ( I ) Individuality] (2) breed, (3) stage of lactation, (4) food, (5) season, (6) time and manner of milking, including fractional milkings, milk from different quarters of udder and relative order of milking a quarter of udder. 5 . Corditions Affecting the Relation of Fat to Total Proteins and to Casein in MiZk.-(1) The breeds studied fall into two general groups; in one case, the ratio of fat to proteins is relatively high (Guernsey and Jersey) ; in the other, relatively lower. Individuals of the same breed may vary considerably in this respect. (2) The ratio of fat to proteins is very uniform through the lactation period until about the ninth month, when the total proteins increase quite rapidly in relation to fat. The ratio of f a t to casein is very uniform, throughout the entire period of lactation] there being a slight increase of casein in relation to fat about the ninth month. (3) Variations in composition of milk due to manner of milking affect the fat more or less extensively but the proteins very little. 6. Conditions A fecting the Relation of Casein to A 1b.umin.-Albumin in milk varies quite widely in relation to casein. The relation varies
1.
IlSO
11. X(>R'I'(lK.
i i ivitli different ljrec:ls, (2:' \\.itti tlifierent individuals of the same breed, \i.ith tiiiie am1 iiianiier oi iiiilking, (4) tlie relation is quite uniform tliiring the first eight or iiiiie nioiitlis of lactation. after which the albumin iiicreases relati\-c.!y more tliaii ~ l i cviiseiii. 7 . .\iefliods j o i , L ' i i / ~ ~ u ! , z t i i i (; .: ' ~ / . ~ ~ i~r i/i d' i ~7.iif,zl I ' v o t e i ? ~ .i ~i z :\'oYiizal iJfil/i.--.111 the c ; of ~l:er
