[CAMERON] VERTEBRATE STRIATED MUSCLE 93 



VII. The Achromatic and the Fibrillar 

 Phases of Myo-Genesis. 



From what has been already stated in the preceding sections 

 of this monograph, it will bé recognised that there are two very distinct 

 stages in the histogenesis of muscle fibrils, namely, the nascent or 

 achromatic phase and the fibrillar or chromatised^ phase. I can 

 find no evidence of the existence of these two very distinct and decided 

 stages having been previously chronicled by writers on the subject. 

 There is no mistaking their existence, however, and I would suggest 

 that a full appreciation of their significance will permit the subject 

 of myo-genesis to become very much simplified. 



What appears then to happen is, that the nascent achromatic 

 material undergoes a mysterious process of maturation or "chroma- 

 tisation" along very definite lines (Fig. 10). Each "line of chrom- 

 atisation" is not a continuous one, but is interrupted in the most 

 definite and characteristic manner into alternate achromatic and 

 chromatic elements, forming the rudiment of a muscle fibril, and at 

 the same time constituting the basis of muscle striation. The writer 

 has previously described and emphasised the existence of achromatic 

 and chromatised phases in the histogenesis of nerve fibres. It is 

 therefore interesting and also significant to note that these previous 

 observations are confirmed by the present results. This rather sudden 

 alteration in the staining properties of the nascent achromatic ma- 

 terial must of course indicate a corresponding change in its chemical 

 properties. It would therefore appear as if some knowledge of the 

 chemistry of the process ought to provide us with a certain degree 

 of enlightenment regarding the exact nature of the process of fibril- 

 lation. 



The fibrils of course increase in number, as more and more "lines 

 of chromatisation" become produced. The result is that the area 

 of achromatic material becomes rapidly encroached upon (compare 

 Figs. 11 and 12 and also 13 and 14). This progress, as these Figs. 

 show, is very clearly demonstrated in cross sections of the muscle 

 fibrils, which appear as groups of intense black dots all over the 

 microscopic field. The term "Cohnheim's areas" has been applied to 

 these — a very objectionable title indeed. In the first place it provides 

 us with no indication as to what the "areas" consist of, and in the 



^This is the most suitable word I can invent to describe this remarkable trans- 

 formation of definite portions of the achromatic material into a chromatic substance 

 readily acted upon by staining agents. 



