LETTERS To the Editor: The trenchant editorial in your October issue on the difficulties of teaching chemistry in a one-year course to high-school students, recalls Sir Harry Lauder in his impersonation of a Scotch schoolboy, when he fishes something out of his pocket and says slyly. "That's a washer. That's what they make motor-cars with." Professor Hauser rightly insists upon experimental demonstrations, which, if properly chosen, can and should arouse enthusiasm in the student; but some kind of coherent explanation must bind the facts together, if interest of the student is to be maintained by comprehension of how the "motor-car" of chemistry works, without resort to obsolete theories or asphyxiation by excessive detail. My own experience in talking to mixed audiences is that the nearer experimental instances come t o the affairs of daily life, the greater the interest aroused in most people. Colloid chemistry touches upon many of the practical happenings in the kitchen and household and shop and farm, and simple explanations for many of these happenings can be given, even though the ultimates are infinities beyond human understanding. We must, of course, distinguish between experimental facts and the changing and often divergent theories set up to explain them. Thus, few doubt the reality of biological evolution, though there is no unanimity of opinion as to how i t was accomplished. Dr. Hauser brands as "definitely wrong" the statement taken from recent high-school chemistry texts "that the addition of protective colloids aids in the digestion of foods, such as the addition of gelatin to ice cream." About 35 years ago I observed, on watching the coagulation of cows' milk in the ultramicroscope, that the formation of coagula was inhibited when I added gelatin or gum arabic, well known even then as "protective colloids." With Dr. J. G. M. Bullowa, I extended these experiments to mothers' milk and found that this more highly protected milk (about 7 times the protection, based on lactalbumin ratio to casein) was not readily coagulated by acid or by rennin, and that the coagula were much smaller than those of cows' milk. An examination of the medical literature revealed that the eminent pediatrician, Dr. Abraham Jacobi (subsequently President of the American Medical Association), had written in his book, "Intestinal Diseases of Infancy and Early Childhood," the following: "But it is not the chemical formula alone which determines the rank of a substance as nutrient. To the equivalents of the chemical formula of caw casein infant mathematics would not There object, did not the infant stomach revolt against it.' is no doubt, therefore, as to the utility of gum-arabic and gelatin as an addition to cow's milk and to children's diet. Not only do they fulfill the indication of diminishing and distributing the particles in caw's milk, but they also officiateas a means of direct nourishment by preventing waste."l
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VOI.I, P. 45.
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Further information can be had in papers by Alexander and Bullowa in the Archives of Pediatrics and the Journal of the American Medical Association, both for 1910, and in Alexander's "Colloid Chemistry," 4th edition (D. Van Nostrand Company, Inc., 1937). Despite differences in theoretical explanation, protective colloids do protect-as we see, for example, in the photographic emulsion. Dr. Hauser's insistence on logical thinking and logical reasoning, and on the value of mathematics in this direction, are both timely. But we must distinguish between pure mathematics and applied mathematics. As the mathematician Sylvester remarked, a pure mathematician is never so happy as when he does not know what he is talking about-for then he is not bound to the exact congruence of his mathematical statements or formulas with the physical facts of a problem. Formulas based on erroneous assumptions generally lead to wrong conclusions, no matter how impeccable the mathematical technique. Sylvanns P. Thompson's "Calculus Made Easy" shows that even "higher" mathematics can be given a local habitation and a name. JEROME ALEXANDER 50 EAST4 1 s ~ STREET NEWYORK, NEWYORR
To the Editor: Referring t o Mr. Alexander's discussion of the effect of protective colloids on the digestion of foods, I would like to offerthe following: I admit that the wording of my address, to which Mr. Alexander refers specifically, was too condensed and therefore perhaps misleading. The complete reference in the textbook referred to reads as follows: "Protective colloids seem to aid in the digestion of food. Most commercial ice aeam contains about '/? per cent gelatin. Careful observations over many years seem to indicate that the gelatin aids in the process of digestion of such foods." I am in full agreement with Mr. Alexander's experiments and literature references as far as various types of milk and their coagulation are concerned. That the protective colloid prevents the formation of lumpy coagula and thus facilitates digestion is well known to every colloid chemist. To the high-school student. however, the why would have to be explained first. It is not, as the text would indicate, that the protective colloid as such aids digestion, hut that i t assists in the distribution of the food to be digested, when i t is coagulated. However, the main reason for the addition of gelatin t o ice cream is to prevent the formation of long sharp, pointed ice crystals which would detract from the creamy smoothness of the product. ERNSTA. HAUSER OF TECHNOLOGY M ~ s s n c ~ u s ~INSTITUTE rrs C m m c ~ MASSACHUSETTS .
