REACTIONS OF FIXATIVES WITH PROTEINS. 



41 



acid solution, tannic acid solution, and Flemming's fluid to 

 aqueous solutions of dried egg-white at various concentrations, 

 and studied the resulting material under the microscope. He 

 noticed that if the solution of egg-white was dilute, fine granules 

 were seen, while with higher concentrations these joined together 

 to form a network of fibres. He made similar observations with 

 peptone and soluble gelatine (probably metagelatine). His figures 

 of the networks produced in soluble gelatine by the action of 

 tannic acid are reproduced here in fig. 4, A, b. Schwarz considered 



B 



s*.^ 



X 









[ 





V, 



>^v ••».. 





- 1 J' V --^ . 



.^ - -.-\ J ^ \}.-\ . \ 



\ is, ■ \.^ .t 







V'w .\-. 







FIG. 4. Protein coagula seen under the microscope. 

 Each scale represents lo/n. 



A, dilute solution of soluble gelatine, fixed by 0-5 % tannic acid. 

 B, ditto, fixed by 6'^o tannic acid. C, egg-white fixed by mercuric 

 chloride (saturated solution in o-6°o sodium chloride); paraffin 

 section, i/x or less. D, ditto, fixed by potassium thiocyanate. (a 

 and B from Schwarz; ^'"^ C and D from Hardy. ^") 



that the granules or fibres lay in a continuous Grundsubstanz . 

 They were more colorable by picric acid than was this interstitial 

 material. 



Schwarz's important work has been very much overshadowed 

 by Hardy's,^^^ and indeed the Cambridge physiologist carried the 

 investigation a good deal further. He worked chiefly with egg- 

 white, but also with gelatine. He caught up a drop of protein solu- 

 tion in a loop of silk thread and placed it in an aqueous solution of 

 mercuric chloride or some other fixative ; he then usuallv embedded 

 it in paraffin and cut thin sections (down to o-6/x). He also used 

 frozen sections and minute, teased fragments of unembedded 



