

i8 9 3. ETIOLOGY OF VEGETAL GALLS. 357 



with the ovipositor, from which it is easy to make them expel a drop 

 of liquid by irritation. The presence of this fluid he considers to be 

 the first essential fact in the order of causation ; and he proceeds to 

 illustrate its mode of action by reference to the analogy which he 

 says exists between it and some well-established facts in animal and 

 vegetable pathology. When the surgeon, charging his lancet with a 

 drop of vaccine lymph, or with fluid " d'une ulceration syphilitique," 

 introduces the point under the skin of a healthy subject, it is 

 invariably followed, whenever morbid action is set up, by the repro- 

 duction of disease akin to that from which the virus has been taken, 

 whatever may be the form of the incision, or the quantity of the 

 fluid inserted. The specific quality of the morbid poison in these 

 cases is, he says, an accepted doctrine — neither the result nor the 

 evidence is questioned. Taking another series of facts, viz., those 

 relating to the stinging of bees, wasps, scorpions, and other animals, 

 he shows that the results, though in many respects akin to one 

 another, are nevertheless specifically different. The swelling in one 

 case is slight and temporary, in another it is large and persistent. 

 It is the same with regard to the attendant pain. That result- 

 ing from the sting of a bee will continue for an hour or two, 

 while, in the case of the scorpion, it may last for years.9 No 

 one, he says, denies the relation of cause and effect in such cases. 

 Why, then, should we do so in that of the specific virus of the Cynips 

 and the resulting gall? Once this first step taken, once the doctrine 

 of a specific poison admitted, and we are in a position, he thinks, not 

 only to explain the occurrence of galls in general, but to account also 

 for their specific forms. No one, he says, has any difficulty in under- 

 standing how the normal forces of the plant vary with the poison, or 

 how all secondary characters are due to the mode in which the poison 

 acts in the developing vegetable tissues. 



This view of Lacaze Duthiers is the one most generally entertained, 

 and it has for its support the concurrent authority of Hofmeister, 10 

 and Darwin," Sir James Paget, 1 - Sir John Lubbock,^ and other 

 distinguished writers. 



Whether or not, however, it can be regarded as the correct one, 

 is, in a measure at least, doubtful. The analogy upon which it rests 

 is by no means perfect. The presence of the ovum (not found in any 

 of the cases referred to by Lacaze Duthiers) is, it may be, as necessary 



9 The injurious effects of the sting of the scorpion are said by Mr. Andrew 

 Murray, F.L.S., to be much exaggerated, the pain being in some cases less than 

 that of the sting of a wasp, and of incomparably shorter duration. See " Science 

 Handbook of Economic Entomology — Aptera." South Kensington Museum, 1877. 



10 " Allgemeine Morphologie der Gewachse," p. 634 (1868). 



11 " Origin of Species," 5th ed., p. 572 (1869), and 6th ed., p. 6. " Plants and 

 Animals under Domestication," 1st ed. (1868), vol. ii., pp. 382-4 418. 



12 " An Address on Elemental Pathology," Brit. Med. Assoc, Aug., 1880.' 



13 " On the Origin and Metamorphosis of Insects," Nature Series, 1874, p. 10. 



