432 



BUEEAU OF ANIMAL INDUSTEY. 



ticks were followed by the fever. There are, however, in both countries, particularly 

 in the more southern and warmer parts of the United States, parts where tick- 

 infested cattle exist in great numbers and do not suffer from acute Redwater. These 

 cattle are, however, natives, and inherit their immunity from the disease while still 

 carrying in their blood its ' * germs. ' ' From them the ticks are known to take the dis- 

 ease to susceptible cattle, either when mixing with these other cattle or grazing over 

 the same ground within a certain period after they have crossed it. These suscep- 

 tible animals have the disease carried to them by the young, or larval, ticks hatching 

 from the eggs laid by those dropping from the former cattle. Ground traveled over 

 by the cattle which carry the disease in their blood remains infected with the disease 

 only so long as it is infested with these larv?e, and this period is limited by the length 

 of time that they can live without food. This again, providing there is no reinfesta- 

 tion, is more or less extended according to climatic conditions — heat and cold, dry- 

 ness and dampness, young ticks being very subject to such variations and capable of 

 living a great while when they are favorable. Ground is said to remain infested for 

 as many as six months in winter and two in summer in the case of the American 

 Redwater tick, of which it is recorded that — ^ 



(1) The delay in the beginning of egg laying is nearly three weeks in winter as 

 compared to twenty-four to forty-eight hours in sunnner.^ 



(2) The time elapsing between the laying of the first and the last egg by a female is, 

 in summer temperature, only a few days, while in winter it may extend over a period 

 of five weeks. 



(3) In winter incubation is almost suspended, and months may elapse before 

 hatching takes place. In summer the normal incubation period is about twenty days. 



(4) Seed ticks (larvae) are capable of existing without food four and one-half 

 months in winter; in summer the time survived was about two months. 



The short summer period does not, I am told by Mr. Hutcheon, C. V. S., actu- 

 ally apply to our local conditions, as there are certain evidences of veldt remaining 

 infected for far greater periods. 



We have recently received some ticks from Porto Rico, which 

 } resemble the Australian form in all essential details, except that the 

 teeth on the internal apophysis — which both Neumann and Fuller dis- 

 cuss and figure as if they were easily studied — have baffled us. These 

 characters may be of value in classification, as claimed by Fuller. On 

 the other hand, we have not found them to be practical working char- 

 acters; and, as the teeth on the external apophysis of Boophilus 

 annulatus are subject to considerable variation, we are somewhat sus- 

 picious regarding those on the internal apophysis. 



The Porto Rican ticks in question when first sent to Washington were 

 much smaller than the North American form, resembling more closely 

 the Australian specimens. After several generations, however, they 

 became more elongate and resembled the North American form so 

 closely that the females can not possibly be distinguished with the 

 naked eye, and a microscopic determination is very uncertain. The 



1 ''The following information is quoted from Bulletin 51 (2d Ser.) of the Louisiana 

 State University and A. & M. College. The Cattle Tick and Texas Fever, by W. H. 

 Dalrymple, H. A. Morgan, and W. R. Dodson. Baton Rouge, 1898." 



2 "In the case of the Bonte Poorten Tick {Amblyomma hebrseum Koch) we find that 

 there was a delay of from two to three months in beginning egg-laying in winter 

 (May to July), and about a week in summer (January)." 



