ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 235 



or membrane of some kind, which prevents escape of the cell contents. 

 We may draw a similar conclusion from the fact that the products 

 arising from the digestion of food particles in Protozoa, although 

 consisting of such freely diffusible substances as glucose and amino- 

 acids, are not washed out." The author discusses the nature of this 

 membrane. " We may conclude that, when examined under normal 

 conditions and at rest, living cells are surrounded by a membrane 

 impermeable to most salts, to strong acids and bases, and also, as shown 

 by osmotic experiments, to glucose and to amino-acids. There are, 

 however, certain crystalloids to which the cell appears to be permeable 

 under all conditions. These are urea, ammonium hydroxide, and some 

 other ammonium salts, certain dyes of low molecular weight, alcohols, 

 etc." " Nothing but a complex system of more than one phase will 

 suffice to explain the changes in permeability which are shown by the 

 surface membrane of the cell." "Since the memlirane is a local con- 

 centration of components of the protoplasm of the cell, there must 

 always be an equilibrium between the two. Hence a change in either 

 involves a change in both." The author goes on to refer to typical 

 physiological phenomena in which membranes of variable permeability 

 are believed to play an essential part. J. A. T. 



Theory of Specific Plasma. — Louis Legraxb {La Selection du 

 Plasma Specifique, Paris, 1916, 183). Chemical analyses, biological 

 reactions, grafting experiments, and other data prove the reaHty of 

 specific plasmas characteristic of different species. There is plasma 

 common to all members of a Metazoan species, and there are varietal, 

 individual, and ancestral plasmas which are not quite so fixed. The 

 former is cytoplasmic, the latter are nuclear. The male gamete is the 

 vehicle of non-fixed plasmas of the individual male organism. The 

 ovum is the vehicle in the main of the fixed plasma. Adaptation is 

 fundamentally a cellular affair, and is effected in the course of de- 

 velopment. The fertilized ovum is unstable, and cell-divisions are 

 required to reach cellular adaptation. The individual plasmas are 

 diluted more and more to the vanishing point ; the specific plasma 

 preponderates over them ; there is a sort of struggle between them ; 

 degenerations and death mark the partial or complete victory of indi- 

 vidual plasma over the specific plasma. From this point of view the 

 author considers some of the great steps in organogenesis. The central 

 fact is the continued chemical adaptation of the ceil to its complicated 

 environment. In the nutritive life of the organism there is a selection 

 of specific plasma, at successive stages (physical choice of food, utilization 

 of the food, on the part of intestinal cells, on the part of hepatic cells, 

 and so on). This selection is not only individual, but racial. It began 

 in the earliest individualities, which selected the most suitable environ- 

 mental materials. In Metazoa the gonads themselves and the details of 

 reproduction are adapted to secure the continuity of the specific plasma. 

 In this connexion the female is much more important than the male. 

 For species and individual alike the central fact is the preservation (by 

 selection) of the specific plasma. That at least is the author's conten- 

 tion, J. A. T. 



