PATHOLOGICAL HISTOLOGY 55 



description, to be more typical of tuberculosis than 

 of Johne's disease. 



Patholog-ical Histolog-y. — Organs for histological 

 examination should be removed from the animal as 

 soon as possible after death, as post-mortem changes 

 rapidly take place. Small pieces of gland and bowel 

 should be placed to harden in methylated spirit, or 

 in formalin -alcohol, or in Mailer's fluid containing 

 ID per cent, of formalin. When one stains for the 

 bacillus, it is preferable to harden in 5 per cent, 

 formalin without the addition of Mailer's solution. If 

 Mailer's solution is used, the bottles should be placed 

 in a cupboard away from the light, to avoid the pre- 

 cipitation of the bichromate. If alcohol is used, it is 

 advisable to start with a weak solution, and transfer the 

 tissue to solutions of increasing strength, since by this 

 means contraction of the tissue is very largely avoided. 

 After twenty-four hours in the hardening fluid, the 

 pieces of tissue are washed in running water for about 

 the same period of time or longer, and to insure 

 thorough washing, it is best to cut the tissue into thin 

 slices before the commencement of this process. The 

 pieces of tissue are then placed in 90 per cent, alcohol 

 for twelve to twenty-four hours, and, if they are not 

 too thick, the paraffin blocks can be completed on the 

 next day by the following procedure : Place in abso- 

 lute alcohol for one hour, and then change into fresh 

 alcohol and leave for the same time ; then transfer to 

 chloroform, xylol, toluol, or carbon bisulphide, and 

 leave for two hours, the solution being changed at the 

 end of the first hour. Before transferring from the 

 alcohol to the xylol or chloroform, the pieces of tissue 

 may be placed in a mixture of these substances. Now 

 remove from the chloroform, and place into the 

 paraffin bath in a mixture of equal parts of paraffin 



