189 



SPECIAL WORK. 



Direct microscopical examination of streak prepara- 

 tions made from the organs and tissues of infected ani- 

 mals, as well as cultural experiments will reveal the pres- 

 ence of microorganisms. In order to ascertain the presence 

 and especially the distribution of organisms within tissues 

 and organs it is necessary to harden these, then to cut 

 sections and finally to stain the sections by suitable meth- 

 ods. 



Hardening. For this purpose alcohol is usually 

 employed and gives excellent, results. The tissue is cut 

 into small pieces which are either transferred direct to a 

 wide-mouthed bottle containing 92-96 per cent, alcohol, or 

 are first placed on pieces of filter paper and then in the 

 alcohol. The pieces of tissue should remain in this alcohol 

 for at least 3 or 4 days, or until it is desired to make sec- 

 tion?, when they are transferred to absolute alcohol for 

 one or two days. The tissue is then hardened and ready 

 for cutting sections. To do tljis a piece of the tissue is at- 

 tached to a small cork by means ot a glycerine gelatin 

 mixture made by warming 1 part of gelatin, 2 parts of 

 water and 4 parts of glycerine. The cork is then securely 

 clamped to the microtome and sections made. The tissue 

 and knife must be kept moist with alcohol and the sec- 

 tions are at once transferred to alcohol by means of a 

 camel hair brush. 



Very satisfactory and rapid hardening can be obtained 

 with a solution of mercuric chloride made by saturating 

 an aqueous five per cent, glacial acetic acid solution with 

 mercuric chloride. The tissue can be fixed in this solution 

 in 4 to 12 hours. It is then passed through a series of 



