September 8, 1905.] 



SCIENCE. 



291 



dangerous coast district that the disease 

 was introduced into Rhodesia and into the 

 Transvaal. On this map which I throw on 

 the screen I have marked out the probable 

 endemic area of this disease, and in the 

 next slide the present distribution of the 

 disease in the Transvaal is also marked out. 



Nature of the Disease. — This disease only 

 attacks cattle, but in them is an exceedingly 

 fatal malady; in every hundred cattle at- 

 tacked only about five recover from the 

 disease. The duration of the disease after 

 the first symptoms have occurred is about 

 ten days. 



The cause of the disease is a minute blood 

 parasite called the Piroplasma parvum 

 (Theiler). This parasite lives in the in- 

 terior of the red blood corpuscles. 



I now throw on the screen a representa- 

 tion of the blood from a case of Rhodesian 

 redwater, magnified about a thousand 

 times, showing these small piroplasmata in 

 the interior of the red blood corpuscles. 

 As in the case of so many of these blood 

 diseases, the parasite causing it is carried 

 from the sick to the healthy by means of a 

 blood-sucking parasite. In this particular 

 disease the tick which most commonly 

 transfers the poison or living parasite from 

 one animal to another is known as the 

 'brown tick,' Bhipicsphahts appendicu- 

 latus. Koch supposed that the common 

 'blue tick' was the agent. The credit be- 

 longs to Dr. Lounsbury and Dr. Theiler of 

 having shown that it is chiefly the 'brown 

 tick' which acts as carrier; but Theiler has 

 proved that B. simus is also able to trans- 

 mit the disease. Without the intervention 

 of a tick, as far as we know at present, it 

 is quite impossible that the parasite of this 

 disease can be transferred from one animal 

 to another. For example, if we take a 

 quantity of blood containing enormous 

 numbers of these piroplasmata, and inject 

 it into the blood circulation of a healthy 



animal, the latter does not take the disease. 

 In the same way, if cattle affected by east 

 coast fever are placed among healthy cattle 

 in a part of the country where none of these 

 'brown ticks' are found, the disease does 

 not spread. It is evident, therefore, that 

 some metamorphosis of the parasite must 

 take place in the interior of the tick, and 

 this new form of the parasite is introduced 

 by the tick into a healthy animal, and so 

 produces the disease. In this particular 

 disease the virus or infective agent is not 

 transmitted through the egg of the tick, as 

 is the case in some of these parasitic dis- 

 eases, but only in the intermediate stages 

 of the tick's development; that is to say, 

 the larva which emerges from the egg of 

 the tick is incapable of giving the disease. 

 What happens is this : the larva creeps on 

 to an infected animal and sucks some of its 

 blood. It then drops off, lies among the 

 roots of the grass, and passes through its 

 first moult. The nympha, which is the 

 name given to the creature after its first 

 moult, is capable of transferring the disease 

 to a healthy animal; that is to say, if it 

 crawls on to a healthy animal and sucks 

 blood from it, it at the same time infects 

 this healthy animal with the germ of east 

 coast fever. In the same way, if a nympha 

 sucks infected blood from a sick animal, it 

 is able, after it has moulted into the adult 

 stage or imago, again to give rise to the dis- 

 ease if placed, or if it craAvls, upon a 

 healthy animal. 



The Life-history of the Brown Tick.—l 

 throw on the screen a slide representing the 

 four stages of the life-history of the brown 

 tick: The egg, the larva, the nympha and 

 the adult or imago. The eggs are laid on 

 the surface of the ground by the adult fe- 

 males, who deposit several thousand at a 

 time ; and these hatch out naturally, if the 

 weather is warm and damp, in twenty-eight 

 days. But this period of incubation of the 



