December 26, 1912J 



NATURE 



477 



method was introduced into practice last year, and 

 only in the experimental manner ; it has not yet stood 

 the' brunt of the severe tests of the practice. 



The experience just now alluded to teaches us that 

 under the conditions of the practice breakdown in 

 immunity will occur. It remains to be seen to what 

 extent they do occur, or, in other words, what per- 

 centage of inoculated horses will be protected against 

 the naturally acquired disease. The same principle 

 was made use of in the preparation of the blue-tongue 

 vaccine, and again recently in the method of inocula- 

 tion against anaplasmosis of cattle, a disease generally 

 known as gall-sickness. This latter was found to be 

 caused by parasites attacking the red corpuscles of the 

 blood. The remarkable observation was made that 

 two ditTerent varieties of organisms could be distin- 

 guished under the microscope, and the tests proved 

 that whereas one species was very virulent, the other 

 one was very much less so, and this latter protected 

 an animal to a great extent against the former. The 

 vaccines used against the various diseases therefore 

 represent by no means anything artificial; they are 

 specially selected germs producing the disease in a 

 milder form, which give a great amount of immunity, 

 but by no means a complete one, owing to the exist- 

 ence alongside of still stronger varieties of the same 

 species or genus. 



A cure or an inoculation against a disease always 

 appeals to the mind of a layman, and more credit is 

 attached to such an inoculation than to other methods 

 of prevention or controlling the disease which perhaps 

 are more rational but more tedious and cumbersome. 

 A good illustration of this is afforded by red-water, 

 which, as many of you will remember, was introduced 

 into the Cape Colony many years ago. In those days 

 measures were taken to stop its spread, but they were 

 of no use, because the cause of the plague was not 

 then known. Only in the beginning of the 'nineties 

 of the last century was it found in America that it 

 was due to a parasite which lived in the red corpuscles ; 

 the parasite developed in the body of a tick, and was 

 transmitted by these to new cattle. 



This was as much an epoch-making discovery as 

 Bruce 's that the trypanosoma disease was carried by 

 winged insects. The statements of the American men 

 of science were subsequently verified in Cape Colony, 

 and when the attention of South African workers was 

 directed to the presence of similar parasites in the blood 

 of South African stock suffering from various other 

 ailments, then it was only natural to conclude that in 

 their propagation ticks also must be responsible. The 

 conclusion proved to be correct. It was further proved 

 that there also existed the theoretical reservoir; it was 

 found that it was the recovered animal itself which 

 remained infected. This fact, so paradoxical as it 

 appears for healthy animals to spread a disease, ex- 

 plains the permanency of infection on our pasture ; 

 although they are immune, they maintain the con- 

 tamination. 



The investigations by Lounsburv into heart-water, 

 a disease caused by an invisible organism which at 

 one time rendered the rearing of cattle and small 

 stock almost an impossibility, more particularly in 

 this neighbourhood, proved definitely that also here 

 ticks were responsible. Once these facts were well 

 established, it was a natural conclusion to expect that 

 the destruction of the ticks would mean the eradica- 

 tion of the disease, iust as the destruction of mos- 

 quitoes meant the disappearance of malaria. This 

 conclusion at one time had only appealed to a limited 

 number of farmers, and it is even at the present time 

 not sufficiently appreciated. Perhaps it is not scientific 

 enough, or there is not enough mystery about it. 



When the terrible disease. East Coast fever, w-as 



NO. 2252, VOL. go] 



introduced into South Africa, the presence of a para- 

 site found in the blood corpuscles was soon recognised, 

 and the conclusion had to be drawn that here again 

 ticks were responsible. This also proved correct. 

 After the species of tick which transmitted the disease 

 had been traced, and their life-history was fully under- 

 stood, and once it had been realised that in this disease, 

 unlike the other caused by intracellular parasite, the 

 immune animal did not represent the reservoir for the 

 virus, it became possible successfurn to combat it. 

 In the course of time the most powerful remedy proved 

 to be the dipping tank, which was decidedly the salva- 

 tion of the Natal farmer, all other methods of stopping 

 the spread in that Colony having failed. For the 

 destruction of the ticks as the root of many evils in 

 stock, the dipping tank must be considered to be the 

 best and most practical means, and its introduction 

 into South Africa is a great scientific attainment. 



Not only in the world of micro-organisms, but also 

 in that of higher developed parasites, we shall find 

 our example for demonstrating the utility of the adop- 

 tion of biological research. I refer to one of the most 

 important farming industries, viz. the breeding of 

 ostriches. We know that one of the main drawbacks 

 are internal parasites, and although the farmer is able 

 to help himself temporarily in a rough and ready way, 

 yet he feels that, in order to combat these pests more 

 successfully, more scientific knowledge is required 

 about the life-history of these worms. As soon as this 

 is established — and I can tell you that good progress 

 has already been made in this connection — practical 

 deduction will be possible in order to build up a rational 

 hygiene for the rearing of the chicks. 



So far I have selected my examples in scientific 

 research and practical application out of a group of 

 diseases due to parasites visible to the naked eye, by 

 microscope, or those that can be traced by means of 

 inoculation experiments. We have, so to say, the 

 cause of the diseases in our hands, and can produce 

 and reproduce them at will. This is the one and per- 

 haps the main reason why in the past, in a consider- 

 ably short time, good progress was made ; we were 

 dealing with problems similar to many others already 

 solved. I will now have to mention a subject where 

 the use of the microscope and all transmission experi- 

 ments into animals failed. It is the disease 

 "Lamziekte" in cattle, to which, in recent years, so 

 much attention has been given by the public, the 

 Press, and Parliament. It has caused terrible destruc- 

 tion, and even threatened to ruin the newly-developed 

 north-western districts. 



The investigations carried out so far in conjunction 

 with Mr. Burtt-Davy. the Government agrostologist 

 and botanist, show that we have to deal with tox'ins 

 which are present in grasses of certain areas. This 

 j is at least our theory, and it is well founded; it is, 

 j however, by no means new, as it has its analogies 

 1 in other parts of the world, and explains the observa- 

 I tions made by farmers in various parts of South 

 Africa ; indeed, it represents the views of many 

 farmers, although not precisely expressed. It is 

 that grasses on certain soils and under certain 

 climatic conditions develop a poison of an ac- 

 cumulative character which only shows its effects 

 on cattle after they have partaken of such 

 grasses for a prolonged period. Actual feeding ex- 

 periments which have been started on various experi- 

 mental stations will bring the proof one of these days. 

 The influence of climate and soil has also recently 

 been brought home bv experiments undertaken in 

 Natal. Some of you will remember that Mr._ Robert- 

 son, of Grahamstown, proved in an unmistakable 

 way that the plant Senccio lafifolln. collected in that 

 part of the country, was found to be very fatal when 



