18 11. HAYS BULLARD 



III general it may be said that the shape of the true interstitial 

 granules indicates that in fresh, unfixed muscle they are composed 

 of a plastic, yielding substance which easily takes the form imposed 

 by surrounding structures of a more resistant nature. Probably 

 the term granule is a misnomer, but it is here used because it 

 has become firmly fixed in the literature. 



KoUiker ('88), Holmgren ('07, '10), Thulin ('09) and Knoche 

 ('09) believed that the true interstitial granules possess a limit- 

 ing membrane. In Weigert, Altmann, Cresylviolett and Nile 

 blue preparations, I have observed nothing which can be taken 

 as indicating the existence of such a membrane. The membrane- 

 like appearance in fresh unstained preparations is, in all probabil- 

 ity, an. ojjtical effect due to differences in refractive index. 



IV. GENERAL OCCURREXCE OF INTERSTITIAL GRANULES AND 



FAT DROPLETS 



General occurrence of true interstitial granules 



Kolliker ('89) described the true interstitial granules as of con- 

 stant occurrence, sometimes in enormous numbers, in the striated 

 muscle fibers' of all classes of vertebrates and insects. Knoll 

 ('91) observed the true interstitial granules in a large number of 

 animals including amphibians, reptiles, birds and mammals. Ret- 

 zius ('09) described his sarcosomes (true interstitial granules) in 

 insects and mammals. Altinann ('94) demonstrated the granules 

 in insects and in the frog. Holmgren ('07-' 10) described Kolliker's 

 granules as occurring in insects and in vertebrates, rabbit, guinea 

 pig, rat and white mouse. 



The large true interstitial granules are included in nearly every 

 description of insect nuiscle. Similar granules in vertebrate mus- 

 cle, although described by the investigators just mentioned and by 

 many others, have frequently been overlooked. This applies not 

 only to text books but likewise to recent original articles. 



The white muscles of the rabbit show, by the Weigert or Alt- 

 mann method, only a few granules or none at all and the red mus- 

 cles may show but a limited number. In the dark fibers of the 

 dog and the gray rat, granules are larger and somewhat more 



