i6 



PRINCIPLES OF GENERAL PHYSIOLOGY 



1 





Fig. 16 shows cells of the gut of Qnuetu; A, after the action of osmic vapour; 



B, after mercuric chloride. Both structures cannot represent that of the living 



cell, and probably neither does. 



Without the neces- 

 sity of further details, 

 it may be said that 

 if we find vesicular 

 (Biltschli) or network- 

 structures in fixed 

 protoplasm, we are 

 not entitled to assume 

 the pre-existence of 

 similar structures in 

 the living btate. 



What, then, are 

 we justified in con- 

 cluding from the ap- 

 pearances presented by 

 fixed tissues or cells ? 

 This much, of course, 

 is clear, that there 

 must have been some- 

 thing present in the 

 living cell to give rise 

 to the fixed structure ; 

 although, without 

 further evidence, we 

 cannot assume that 

 there is any similarity 

 between the two. 

 Moreover, when we 

 find in cells of the 

 same kind, fixed, 

 stained, and treated 

 in the same way, the 

 presence of something 

 in certain cells absent 

 from others, we may 

 reasonably draw the 

 conclusion that some- 

 thing has happened in 

 the first which has 

 not happened in the 

 second. On the other 

 hand, we must not 

 assume that what we 

 see is the same thing 

 as the change which 

 had taken place in the 

 cell before fixation. 



To take an iiistuin.-, 

 Fig. 17 represents the 

 Purkinje cells of the 

 dn^'s cerebellum, before 

 and in different stages 

 of fatigue, produced by 

 muscular work. \W 

 notice that there is, at 

 first, an increase of some 

 substance which stains 



Fi<;. 17. CHANGES IN THE PURKINJE CELLS OF THE DOG'S 



CKKKKELM-M RESULTING FROM MUSCULAR EXERCISK. 

 1. Normal cell. 



2 to 4. Progressive increase in substance staining with inethylene blue. 

 5. l.:ii i-r stage (fatigue), disappearance of tbe staining substance. 

 (!. Still further stage of fatigue. 



With the exception of No. C, all were stained together, by Held's method, 

 on a single slide. 



(Dolley, 1909, figs. 1, 2, 3, 4, 9, 10.) 



