ELEMENTS OF STRUCTUltE. 73 



and under favourable circumstances, it is possible to penetrate somewhat 

 more deeply into the chemical constitu- 

 tion of these most important of the ele- 

 ments of form. 



Let us first, then, inquire into the 

 constitution of the cell-body. We have 

 already seen in one of the preceding sec- 

 tions that this is originally formed of 

 protoplasm. In speaking of the latter *' 



we described it as a tough, viscid, or ** 



. , , , ' , / i Fi - 65. Lymphoid cells, 1-4, nn- 



niUCOld Substance, consisting OI a peculiar changed; 5, the nucleus and mem- 



albuminous compound, which coagulates ^^SB** S&F*l VB 



at death, and also when heated up to a cer- and ii; 12, it has broken up into six. 

 tain point; which becomes further swollen pieces; 13) fre 

 up or gelatinised by the action of water, but not dissolved. This is 

 about all we know, at present of this important compound protoplasm. 

 The granules which lie embedded in the homogeneous substances of the 

 latter in greater or less quantity, consist partly of coagulated albuminous 

 matters, partly of neutral parts, and more rarely of pigments, especially 

 melanin. That mineral constituents are also present need hardly be 

 remarked. 



In many cells the protoplasm is transformed gradually into various 

 other modifications of the protein compounds. Thus, instead of it the 

 mature blood-corpuscle is composed of watery haemoglobin, the formative 

 cell of the fibres of the lens likewise of an albuminoid known as globulin. 

 Other cells again contain mucin or allied substances, as for instance colloid, 

 and it often occurs that the original cell-body is converted by a loss 

 of water into one of the more solid modifications of the albuminoid 

 group, for instance into keratin, found in the older cells of epidermis 

 and nail tissue, &c. However imperfect our knowledge at present may 

 be, it must still be considered of importance to know for certain that 

 those more remote descendants of the albuminoids, as we meet them, for 

 instance, in glutin and elastin ( 15)., never form the proper body of an 

 animal cell. 



Ferments, also, are probably of frequent occurrence in the bodies of cells. 

 Thus we find minute molecules of pepsin e in the protoplasm of the glan- 

 dular cells of the stomach, and allied matters in the elements of the in- 

 testinal glands. 



We have also hydrocarbons presented to us in hepatic cells in the form 

 of granules of glycogen ( 16). 



Deposits of neutral fats are likewise of extremely common occurrence 

 here. Granules and globules appear at first in the various kinds of cell- 

 substance, gradually forming in seme cases large drops, which may eventu- 

 all} r displace almost the whole of the latter. And although it cannot be 

 doubted that most of these fatty compounds are taken up into the body of 

 the cell from without, it must still be regarded as extremely probable that 

 a formation of fat can be brought about in the cell itself by the splitting 

 up of its proper albuminous body. 



With the exception of the salts of lime, formed deposits of inorganic 

 substances do not occur in the bodies of cells. 



In turning now to the consideration of the chemical constitution of the 

 surface of the cell, we must remember that very generally the enveloping 

 layer of protoplasm has been hardened, now more, now less, through con- 



