4 FIRST LECTURE. 



Here, where the mechanical analysis terminates, the optical 

 begins, by means of the microscope. The latter is an extra- 

 ordinarily delicate one ; the fragment, which the anatomist's 

 scissors are unable further to divide, now proves to be infi- 

 nitely compounded ; it may still consist of thousands of the 

 smallest elements. 



These elements are again, in their turn, cells or their 

 derivatives. 



Thus, this structure, which forms in an independent manner 

 the body of an amoeba, now constitutes our tissues, although 

 in a very conditional independence. The cell has, therefore, 

 entered into the service of a mighty unity ; it has to sub- 

 ordinate and conform itself; nevertheless, the thing remains 

 a living individual, comparable to the officer of a modern 

 state department. As he fulfils his individual duty in the 

 service and as a member of a great whole, so, also, does the 

 small cell labor unremittingly until its death. 



It appears of interest that these very small living foundation- 

 stones in the body of the higher animals always form cells, and 

 that the cytodes of Haeckel have disappeared. 



We have just said that the cells of the human organism 



were very small. Their diameter varies, in fact, 



a & from 0.076, 0.0375, 0.0228 down to 0.0057 mm. 



Thus it becomes possible that a small particle 



of the substance of the body, about a cubic milli- 

 metre, may contain an extraordinary multitude 

 of them. It has been computed that such a 



\{°] 

 *•-«. 





particle of space of the human blood is capable 

 of containing five million red cells, though it is 

 true they only measure 0.0077 mm. 

 e '-^\^ 1 The cells present very considerable variations. 



The latter are gained subsequently with the devel- 

 ^0P _ opment of the body. In the earliest period of 

 ^ ! 9 embryonic life they were all still very similar. 

 ceUs'^vftiTnucl'eus The primitive form of a cell is that of a globe 

 andprotopiasma. or of a body approximating a sphere. Thus ap- 

 pear the cells d, e, g, b of our Fig. 4. The cell, also, from 



