428 
NOCARD AND ROSSIGNOL. 
its effect through tuberculin reaction. The duration of this 
period is variable ; in our experiments, where the chances of 
infection were brought to a maximum, the period was from 19 
to 32 days for contamination by inhalation, and from 32 to 
48 days for contamination by ingestion. With the condition of 
natural contagion it is certain that the period of incubation will 
be considerably longer. 
If a recently purchased cow shows a reaction to tuberculin 
within 30 days following the sale, the veterinarian is justified 
in concluding, that, according to all probabilities , this cow was 
infected before the sale. 
2d. One is often embarrassed in ascertaining the age of the 
tubercular lesions found at the autopsy ; our experiments do not 
offer a complete solution of this problem ; however, should the 
lesions be mollified or calcified, no matter what their extent is, 
so slight and so limited as they" may be, the veterinarian will 
be hereafter enabled to state, in all certainty, that those lesions 
have been in existence for more than fifty (50) days. 
PLANTS POISONOUS TO STOCK.* 
The year-book of the Department of Agriculture for 1900 
contains an interesting account by Mr. V. K. Chesnut, of the 
Division of Botany, on some of the losses sustained by stock- 
raisers on our Western and Northwestern stock ranges by stock 
eating certain poisonous plants indigenous to those regions. A 
synopsis of Mr. Chesnut’s account is here reproduced for the 
benefit of the readers of the Review. 
The principal causes assigned by Mr. Chesnut for plant¬ 
poisoning of stock is the scarcity of food which at times pre¬ 
vails over large areas of our Western ranges. Stock that in times 
of a plentiful supply of forage would not partake of the poison¬ 
ous plants are, in periods of scarcity, compelled by hunger to 
eat them. It is a fact well known to every toxicologist that 
plants which are most poisonous usually present the most succu- 
* Prepared for the Review by Dr. W. J. Martin, Kankakee, Ill. 
