32 PROTOPLASM AND THE CELL 



(hypothetical) " vital" particle. Fat has not been found in the nuclei of 

 cells. In the former case, as adipose tissue, the droplets of the tri- 

 glycerides of palmitic, stearic, and oleic acids largely take the place of 

 the cytoplasm of connective-tissue cells, distending the cell and crowding 

 the nucleus and centrosomes so far to one side that they often are scarcely 

 visible. This might be called the mechanical occurrence of the fats as 

 proximate principles. The other case is more obscure, and, in fact, 

 uncertain. It is, however, probable that fat in some form and amount 

 enters into the composition of all protoplasm, the most likely form being 

 the little-known substance lecithin. This is a very complex body discov- 

 ered by Gobley and Diaconow, best classed as a fatty material, but made 

 up of glycerin in combination with phosphoric acid, the three fatty acids 

 more or less, and the cholin discovered by Strecker. Lecithin is most 

 abundant in nerve-tissue, but seems to be a constituent of all cells. It is 

 especially conspicuous apart from the nerves, in the blood corpuscles, 

 muscles, bile, and milk. Of the function of lecithin in living matter we 

 know little or nothing, but that it takes part with proteid and carbo- 

 hydrate in the basal vital phenomena there is little doubt. Some have 

 deemed it an important constituent of cell-walls, supposing that it deter- 

 mines more or less the osmoses in and out of the cell. Its formula is 

 approximately C^H^NPOg, which has interest at least as indicative of 

 the elements entering into its composition. 



The carbohydrates are the fourth class of protoplasmic constituents we 

 need discuss. They all contain hydrogen and oxygen in the proportion 

 in which these elements constitute water (two to one), and carbon in 

 varying amounts. Carbohydrates, like fats, exist in the nuclei of cells, 

 if at all, only in minute amounts too small to have been found. Our 

 knowledge of the chemistry of the carbohydrates in its completeness is 

 unlike that of the proteids, but their biochemistry is but little less vague 

 than that of the proteids. Three classes of carbohydrates are represented 

 conspicuously in the protoplasm of animals, the glycoses (monosac- 

 charides), the saccharoses (disaccharides), and the amyloses (polysac- 

 charides). The chief glycose of protoplasm is dextrose, which exists in 

 animal bodies to the extent of 0.1 per cent., and often much more. 

 Another name for dextrose is grape-sugar, but it must not be confused 

 with dextrin, which is a polysaccharide, a cleavage-product of the hydra- 

 tion of starch. The formula of dextrose is C 6 H 12 O 6 , and, as its name 

 implies, it rotates the plane of polarized light, as seen in the polarimeter, 

 toward the right. Dextrose is made in animal bodies from the hydrolysis 

 of starch, of the disaccharides, from proteid, and by the hydration of 

 glycogen, the form of starch found in animal protoplasm. Its important 

 use is evidently to furnish motive energy to the organism, through its 

 oxidation in the muscles and other organs. The most abundant sac- 

 charose or disaccharide found in animals is lactose, C 12 H 22 O n . This has 

 not been isolated from any tissue of the body save that of the mammary 

 glands during lactation; it has been found in the amniotic fluid, and 

 sometimes in the urine soon after parturition and after weaning. By 



