5 o6 THE POPULAR SCIENCE MONTHLY. 



The general properties of protoplasm may be readily observed 

 in the simplest organic forms, like the Amoeba, that are usually 

 described as simple masses of protoplasm without structure or 

 any distinction of parts. It should be remarked, however, that nu- 

 merous species of Amoeba have been described, differing in form 

 and to some extent in habits, and there may also be differences in 

 their protoplasm which we are unable to detect with our present 

 means of investigation. 



Under the low powers of the microscope an Amoeba appears as 

 a semi-transparent, jelly-like mass, which glides along with a 

 flowing movement of its apparently homogeneous substance, send- 

 ing out armlike projections from any part of its body to close 

 around substances which it can feed upon, and rejecting other ma- 

 terials unsuitable for its nutrition. The processes of prehension, 

 digestion, assimilation, respiration, excretion, and reproduction 

 are carried on by the entire body, or by any part of it indifferent- 

 ly. The body of an Amoeba, as we observe it, is not, however, a 

 simple mass of protoplasm, as it evidently contains particles of 

 undigested food, with particles representing the various stages 

 the elements of the food pass through in being built up into pro- 

 toplasm, together with the various waste products on the way to 

 be excreted, so that what we call protoplasm, as represented in an 

 Amoeba, contains many extraneous substances ; and substantially 

 the same statement may also be made in regard to the differen- 

 tiated protoplasm of the higher plants and animals. 



From this it must be seen that it is practically impossible to 

 obtain samples of pure protoplasm for analysis, and, even if this 

 could be done, a chemical analysis of living protoplasm can not be 

 made ; but there is, however, evidence to show that there must be 

 a wide difference in the chemical properties of living and of dead 

 protoplasm. Carmine and other coloring matters, for example, 

 do not color living protoplasm, but give a brilliant stain to dead 

 protoplasm ; and other observations show that living substance has 

 properties that interfere with or limit the ordinary chemical and 

 physical reactions of dead matter. 



There are other considerations in regard to the composition of 

 protoplasm which require a reference to the food of the higher 

 animals, which is usually said to consist of the so-called proteids, 

 fats, and carbohydrates, to which should be added certain mineral 

 constituents or salts, with oxygen introduced by the lungs. These 

 groups of food-stuffs have not the physiological significance that 

 was formerly attached to them, and they do not represent definite 

 chemical compounds which have a specific role in the processes of 

 nutrition, as each group includes a great variety of complex com- 

 pounds. The proteids or albuminoids, as they are sometimes 

 called, are a group of organic substances containing carbon, hy- 



