ANTHRAX 103 
greatest amount about them. Free-lying anthrax rods will be surrounded by a thick 
envelope of the same substance. M’Fadyean states that he has never found this reac- 
tion in animals dead from other diseases. The peculiar coloring, he states, in some 
cases may be observed without the aid of the microscope. Our experience with it has 
not been so satisfactory. 
Thermoprecipitation. This method was formulated for practical 
work by Schutz and Pfeiler. It was especially advocated by Ascoli 
for the diagnosis of anthrax. It has been tested by a number of 
laboratory workers and as a rule highly recommended. The method 
is based on the fact that anthrax bacteria, or their decomposition 
products, present in the bodies of animals dead of anthrax, contain a 
precipitinogen which, when brought into contact with anthrax 
immune serum, produces a precipitate at the point of contact. Pickens 
describes the method in detail and concludes that it is a reliable 
means for the diagnosis of anthrax. It was found, however, by 
Pokschischewsky that this reaction took place in cases of infection 
with certain of the pseudo-anthrax organisms. 
Method—tThe principle of this test is based on the fact pointed out by Kraus in 
1897, that an immune serum when brought into contact with its corresponding antigen 
will produce a precipitation at the point of union of the two fluids. The first fluid, the 
immune serum, is difficult to produce. The technic was first worked out by Ascoli. 
The selection of the animal for the production of this serum is an important problem 
to decide. According to Ascoli, Schutz and Pfeiler and others, the ass is the most 
desirable animal. However, good sera have been produced from the horse, mule, cow 
and rabbit. Varying degrees of success have been obtained with the dog, sheep, goat 
and guinea pig. 
The selection of the animal is important as only certain individuals produce a proper 
serum. It is stated by Schutz and Pfeiler that out of one lot of thirty animals only 
three were found that produced a satisfactory serum. According to Ascoli and others, 
the serum of certain normal animals, especially the horse, is apt to produce a precipita- 
tion when brought into contact with salt solution, carbol salt solution, distilled water 
or bouillon. The serum of the animal to be immunized should be tested with reference 
to this quality. 
The test requires an immune serum and the antigen. The animals are immunized 
by repeated injections of attenuated, slightly virulent and virulent cultures of Bact. 
anthracis beginning with the attenuated culture. Several injections are necessary. 
They may be made subcutaneously, into the abdominal cavity or intravenously. The 
injections are made about a week apart. It requires several weeks to obtain a satis- 
factory serum. The blood should not be drawn from the immunized animal for at 
least ten days after the last injection. 
To obtain the serum the blood is drawn in the usual way and allowed to clot and the 
clear serum drawn off. The serum must be perfectly clear and not colored with 
hemoglobin. 
