INTRODUCTION. vii 



gelatine-yielding substance. So that the matter which appears to be the essential 

 foundation of both the animal and the plant is the proteid united with water; though 

 it is probable that, in all animals and plants, these are associated with more or less 

 fatty and amyloid (or starchy and saccharine) substances, and with very small quanti- 

 ties of certain mineral bodies, of which the most important appear to be phosphorus, 

 iron, lime, and potash. 



" Thus there is a substance composed of water and proteids and fat and amyloids 

 and min:ra1 matters, which is found in all animals and plants, and, when these are 

 alive, this substance is termed jDroio^jfajjm." 



As yet wo know almost nothing of the chemical nature of animal protoplasm. 

 Microscopically it does not differ in appearance from vegetable protoplasm, and yet 

 the latter has been found by Reinke to contain over forty proximate constituents. 

 Hence it seems reasonable to infer that animal protoplasm will on further analysis be 

 found to be an exceedingly complex substance, and not properly- comparable with a 

 particle of white of egg. The following account of the chemical composition of pro- 

 toplasm in general is from Carnoy : " Protoplasm is a complex mixture of chemical 

 species. The patient and minute researches of later years have resulted in the dis- 

 covery, in typical protoplasm of joung and active cells, the following substances which 

 we should consider as the essential elements of the living matter : 



1. Albuminoid substances (a vitelline and a inyosine at minimum). 



2. Phosphoric substances (lecithine and nucleine). 



3. One or several liydrocarbonated substances (such as glycose, dextrine, glycogens). 



4. Soluble ferments (diastase, pepsine, inversive ferment, emulsine). 



5. Water (of constitution and imbibition). 



6. Mineral elements (salts, sulphates, phosphates or nitrates of potassium, calcium, 



and magnesium). 



" We should also call attention to the recent analyses made by Reinke and Rode- 

 wald (1881) on the plasmodium of ^thalium septicum, by which they found, besides 

 some accidental principles, the elements above mentioned. These analyses, as also 

 the microchemical researches of Zacharias (1881-83), have besides revealed to us a 

 new element of protean {pjroteiqtie) nature, that of plasiine, which seems to fill an 

 essential role. Finally, we may mention the researches of Mayer and Baginski, which 

 n;ive a new category of soluble ferments : we refer to coagulent ferments, or jjresiires 

 (Labferment). These bodies have already been verified in a quite large number of 

 animal and vegetable cells, which seem, like their congeners, indispensable to the 

 accomj)lishment of certain cellular phenomena." 



We know that potentially the protoplasm of different kinds of cells exerts widely 

 different forces and capabilities. A liver cell secretes bile, a pancreas cell pancreatic 

 fluid, the cells lining the stomach gastric fluid, and an ovarian cell the white of an 

 civg. One egg-cell may become a mollusc, another a man, whose brain-cells are the 

 medium of the intellectual power which enables him to write the history of his own 

 species, and to be the historian of the forms of life which stand below him. 



The simplest, most primitive form of a cell, when without a nucleus or nucleolus, 

 is called a ctjtode. The Monera, which are the lowest animals, have no nucleus, and 

 have therefore been called by Haeckel cytodcs. The existence of cytodes, however, 

 cannot yet be accepted as a settled fact ; all the evidence is simply negative, and foiTOS 

 which once were sujjposed to have no nucleus (c. g. Radiolaria) have been recently 



