619 



Nachdruck verboten. 



Preliminary Note on the Post-Enil)ryonal History of strii)ed 

 Muscle Fibre in Mammals. 



By Alexander Meek, M. Sc, Durham College of Science, 

 Newcastle upon Tyne. 



It is now some seven years since I began to interest myself 

 in the changes taking place in muscle during growth. 1 was at 

 that time giving lectures to farmers on the Natural History of the 

 Farm Animals , and when lecturing on feeding my thoughts were 

 directed to answering the question — how far is it possible for the 

 farmer to form flesh in his stock? Are the fibres added to after birth 

 or do they simply hypertrophy? It is only recently that I have had 

 an opportunity of trying to give a solution by actual investigation, 

 and as the results I have obtained so far bear one another out in 

 an important point I think it well to present a preliminary communi- 

 cation on the subject. 



The starting period of growth or post-embryonal existence is of 

 course in Mammals a very unequal one, and a larger number of types 

 must be examined before a general statement is possible. But in the 

 Field Mouse (Mus sylvaticus), the Cat and the tame Rat, hyper- 

 trophy of the fibres occurs accompanied by a reduction 

 in their number and I should think that this will be found to 

 be true of all the Mammals, if not before, from a stage not long 

 after birth. 



It is convenient in speaking of growth changes to distinguish 

 between proliferation of cellular elements and growth of these ele- 

 ments. And we cannot do better than borrow from Pathology the 

 terms suggested by Virchow: hyperplasia for cell multiplication 

 and hypertrophy for cell growth. For striped muscular tissue 

 then we might say that during growth it undergoes hypertrophy 

 accompanied by aplasia. 



The muscles I have examined are 1) the outer head ofthe tri- 

 ceps of the Field Mouse, choosing for comparison a nestling and a 

 pregnant adult. The middle third of the muscle was carefully cut out 

 in each case, stained in borax carmine in bulk, differentiated in acid 

 alcohol and cut into transverse sections. These were spread in succession 



