88 THE MICROSCOPE. 



the effects of this chemico-gelatinous injection. Where so much wet 

 abounds, gummed paper is apt to come off. 



When dry, it is sufficient, for the purpose of brief examination by 

 the microscope, to wet the surface of a preparation with clean oil of 

 turpentine; immediately after examination, it should be put away 

 carefully in a box, to keep it from the dust, until it can be mounted in 

 Canada balsam. 



The bichromate of potash is greatly superior in colour to the 

 chromate, which yields too pale a yellow ; and subsequent experience 

 has proved that the acetate of potash frequently effects its liberation by 

 destruction of the capillaries, and this even long after the preparations 

 have been mounted in Canada balsam; perhaps this may be owing 

 to some chemical action of the acetate of potash upon them. 



I would suggest the substitution of the nitrate for the acetate of 

 lead, as we should then have, in the liberated nitrate of potash, a 

 valuable auxiliary in the process of preservation. 



Although highly desirable, as the demonstrator of the capillaries of 

 normal tissues, I do not think this kind of injection fitted for morbid 

 preparations ; the infiltrated gelatine producing appearances of a puz- 

 zling kind, and calculated to mislead the pathologist. 



In preparing portions of dried well-injected skin for examination 

 by the microscope, I have tried the effect of dilute nitric acid as a cor- 

 roder with very good results. But, probably, liquor potassa would have 

 answered this purpose better. 



When size-injection is to be employed, coloured either with ver- 

 milion or the chromate of lead, the animal should be previously pre- 

 pared by bleeding, to empty the vessels ; for if they be fiUed with 

 coagulated blood, it is quite impossible to transmit even size, to say 

 nothing of the colouring matter. Hence the difficulty of procuring 

 good injections of the human subject. 



But with the chemico-gelatinous injections no such preparation is 

 necessary ; and success should always be certain, for the potash liquefies 

 the blood, while constant and long-continued pressure by the syringe 

 drives it through the parietes of the vessel into the cellular tissue. 

 The large quantity of infiltrated blood — the invariable concomitant of 

 Mr. Goadby's pi-ocess — characterises it from all other modes of inject- 

 ing, and is a distinctive feature of the preparations. 



Still another plan has been suggested. It consists in adding a 

 quantity of sulphuric ether to the finely levigated colouring matter, 

 which is also first ground or mixed with linseed-oil, in the manner em- 

 ployed by painters. Upon this plan (as well as upon the last named) 



