V ~ L7, . No. 7
A LEEUWENHOECK MICROSCOPE
1673
showed was "endowed with as great perfection in its kind as any large animal" and proved to breed in the regular way of winged insects. He even noticed the fact that the pupa of the flea is sometimes attacked and fed upon by a mite-an observation which is said to have suggested the wellknown lines of Swift. Because of the fine example of scientificmethod and technic which he set in the prosecution of bioIogical research, Leeuwenhoeck well deserves the title "father of scientific microscopy'' which has been bestowed upon him. His publications consist of 112 papers in the Philosophiull Transactions of the Royal Society and twenty-six in the Memoirs of the Academy of Sciences of France, to which body he was elected a corresponding member in 1697. His collected works were published in Dutch and in Latin, each in seven volumes, shortly before his death and an abridged edition appeared in English in two volumes about seventy-five years after he died.
Cellulose in the Light of the X-Rays. In his Friday evening discourseon Jan. 24th a t the Royal Institution, on "Cellulose in the Light of the X-Rays," Sir William Bragg stated that when a fine pencil of X-rays traverses a fiber of any kind, cotton, hemp, ramie, jute, or such like, the mode of scattering indicates that cellulose is composed, in large part a t least, of a mass of small nystale. That the same X-ray diagram is obtained from all fibers, even from animal cellulose, shows that we are dealing always with one and the same substance. It can further he deduced that there is in each crystal a periodicity parallel to the direction of the fiber: and this auantitv can he de~. termined exactly. The essential feature of the construc&n for cellulose suggested by both X-ray and by chemical evidence is the long chain of many links. The honds that tie the links together are far stranger than those that tie the chain together; those that keep each of the cellulose chains together are as strong as the bonds in the diamond. Indeed, how could a thread carry a suspended weight unless there were great forces in play? But the side-to-side forces are far from being so strong. There seems ground t o suppose that bundles of these long chains form "crystallites." small crystalline masses of which the cellulose is largely composed. When the thread is stmtched the X-rays show that these bundles go more and more into line. When the stress is too great the hundles begin to slide past one another, and if the force is too great, they let go and the thread breaks.-Nature Lead Arsenate Sprays. In recent years lead arsenate solutions have been extensively used as insecticide sprays, and a leaflet issued by the U. S. Department of Agriculture describes experiments by H. S. Swingle an the effects of such sprays. It was found that, a t low concentrations af equivalent arsenic content, arsenious and arsenic acids are equally toxic t o peach foliage. At higher concentrations arsenic acid is the more toxic. Arsenic acts as a cumulative poison within peach leaves. The minimum concentration of arsenic acid toxic to veaeh foliaze - contains the eauivalent of 0.0012 ver cent of arsenic pentoxide. Acid lead arsenates containing less than 0.25 per cent of arsenic pedtaxide in water-saluhle form gave minimum foliage injury. Nothing of practical importance is gained by further reduction in soluble arsenic. Lead arsenate cannot he used upon susceptible plants without the addition of some material to prevent burn-
