TISSUES OF THE BODY. 303 



this we may convince ourselves very easily), in fishes and amphibia, of 

 aggregations of simple elongated fusiform and at times branching cells. 

 The same is the case in the embryos of the higher vertebrates. In the 

 latter, however, these cells unite more intimately at a subsequent period 

 to form the common substance of the band. But we may still render 

 the boundaries of the various cells visible here also by artificial means 

 (Eberth). 



173. 



Let us now turn to the growth of muscle. 



Embryonic muscular fibres, as we have already mentioned in the 

 previous section, are considerably finer than those of the infant, and their 

 diameter in the latter is far less than in the adult. 



According to Hart ing's accurate measurements, the muscle fibres of the 

 adult appear about five times as thick as at the time of birth. This 

 increase in length and breadth is brought about by the reception of new 

 particles between those already present in the fleshy substance, or, as it is 

 the custom to say, by intussusception. 



But the fibres of growing muscle become not only larger, but their 

 number also increases, as was demonstrated beyond gainsaying by 

 Budge, by experiments on the sural muscles of a frog's leg. We are 

 indebted to Weismann also for further interesting information on the 

 same point. According to the last-named observer, the growth of the 

 muscles of frogs takes place only in part through increase in thickness of 

 the fibres originally present ; there occurs, besides, a considerable augmen- 

 tation of the number of the latter by a process of longitudinal division. 

 This process is ushered in by an active proliferation of the nuclei or 

 muscle corpuscles (Muskelkbrperchen) in the old fibre, so that we soon 

 meet with regular columns of the former arranged one over the other, 

 while the fibre itself becomes flattened and widened. Subsequently to 

 this the fibre splits into two threads, in each of which the process just 

 described is repeated, so that out of one old muscle element a whole 

 group of new ones eventually takes its rise. Each of the new fibres 

 then attains its typical diameter through that growth from within, which 

 has already been referred to. 



In full-grown frogs, also, during their winter torpidity, we may see a 

 lively regeneration, with fatty degeneration of the previously existing 

 muscle fibres (Witticli). In this case, likewise, the same process of multi- 

 plication was observed by Weismann. 



Great interest attaches further to a discovery made by Lenker, that an 

 extensive -destruction of human muscle fibres takes place during typhus 

 fever, combined with rapid multiplication of the muscle corpuscles and 

 connective- tissue cells. This is due to a peculiar degeneration, and is fol- 

 lowed by energetic regeneration of the elements on recovery. The pro- 

 cess is probably the same as that observed in the hibernating frog. 



This luxuriant growth of the muscle corpuscles takes place, besides, in 

 other states of irritation of the tissue. 



From these facts, few though they be, we may infer that muscle 

 fibres are by no means so persistent structures as was formerly tacitly 

 agreed to. 



The uterus of pregnant women offers us a good opportunity of setting 

 on foot interesting investigations as to the nature of the growth of the 

 elements of unstriped muscle. As is well known, the organ in question 



