24 



NATURE 



[August 2, 



appointments in the Civil Service. The application of 

 scientific principles to engineering is the special feature 

 of our age, and instruction in these principles, and 

 practical training in their application, should be part of 

 the training of every engineer ; and this can only be 

 acquired in a properly-equipped school. A want of 

 familiarity with details will surely be remedied, but a 

 want of scientific knowledge will be a lasting cause of 

 danger to the public. 



Yours very truly, 



George Francis Fitzgerald. 



THE GAPE WORM OF FOWLS (SYNGAMUS 

 TRACHEALIS). 



IN the Bulletin of the Buffalo So-iety of Natural 

 Sciences, vol. v. No. 2, 1886-7, is a paper by Dr. 

 H. D. Walker, which does not appear to have been 

 noticed in this country, on " The Gape Worm of Fowls 

 {Syngamus irachealis)." The writer claims to have dis- 

 covered that the common earthworm (Lumbricus ter- 

 restris) is the intermediate host of this well-known 

 parasite, and to have observed it in all stages of its 

 development. He further suggests the use of common 

 salt on infected poultry runs to secure the extermination 

 of these noxious pests by destroying the worms which 

 harbour and distribute them. 



The series of experiments by which he has arrived at 

 his conclusions are interesting, and afford strong presum- 

 tive evidence of their correctness. The earthworms were 

 carefully dissected and examined, the embryonic form of 

 Syngamiis being found in them, " differing but slightly in 

 structure, so far as can be discovered from the embryo 

 which has passed through one moult after the egg has 

 hatched in water." 



The question may be asked : Why should it differ at 

 all if it is the same? It may be suggested that earth- 

 worms are themselves subject to various intestinal para- 

 sites and that the embryonic forms of many species and 

 even genera are scarcely distinguishable from each other; 

 but with a view to obtaining corroborative evidence Dr. 

 Walker fed some chickens with worms obtained from a 

 place where Syngamiis had not been noticed. These 

 chickens did not develop the gapes. An examination of 

 worms from this spot showed them to be free from 

 embryos such as were found in others. The double 

 observation certainly points to the probability that in the 

 first instance the embryo of Syngamus had been rightly 

 recognized. 



Embryos were also found in the oesophagus and in the 

 lungs of birds to which earthworms taken from an infected 

 locality, but carefully washed and cleansed externally, had 

 been given. 



The only link apparently wanting to complete the chain 

 of evidence is to determine the manner in which the 

 parasite (if it be truly the embryo of Syngamus) makes 

 its way into the intestinal canal of the earthworm. 



Dr. Walker concludes that it is taken in with its food. 

 His evidence upon this point is chiefly negative. Eggs of 

 Syngamus were placed on damp earth in a dish to which 

 living earthworms were added a fortnight later. After 

 ten days chickens were fed with these worms, but were not 

 attacked. This experiment would have been more com- 

 plete and perhaps conclusive if the worms had been 

 supplied at the same time with vegetable food. Unless 

 the worms were fed, the only means of entry for the 

 embryos of the parasite must have been by boring through 

 the outer integument of their bodies, which is not 

 suggested. 



Dr. Walker notices and examines somewhat critically a 

 paper by Dr. Pierre Megnin, published under the 

 auspices of the Entomological Society of London in 1883, 



in which the author, after a minute inquiry into the 

 history, habits, and development of Syngamus trachealis, 

 came to the conclusion that the epidemic of gapes is 

 spread, first by " food or drink which has become infested 

 with eggs or embryos ; secondly, (by) the diseased birds 

 themselves, which are constantly disseminating the eggs 

 of the parasite ; and therefore all other living agents, 

 perfect insects, larvae, or mollusks (for example, the larvae 

 of ants, which are the habitual food of young pheasants, 

 have been suspected, with some appearance of reason) 

 may be acquitted of any share in spreading the disease." 

 The American author disputes these conclusions. Admit- 

 ting that the eggs will hatch in water, and that the 

 embryos may be taken in by birds drinking infected water, 

 he finds no instance, after repeated experiments, in 

 which eggs swallowed by a bird have produced the 

 disease, and although he thinks that exceptional cases 

 might occur, he concludes that the instrumentality of the 

 intermediate host is not ordinarily dispensed with. This 

 is the only material point in which Walker differs from 

 Megnin, and there is nothing in Walker's discoveries to 

 impair the accuracy of Megnin's observations, so far as 

 they go. Dr. Walker's observations on the structure and 

 development of the parasite from the egg through its 

 embryonic stages agree substantially in all other respects 

 with those of Dr. Mignin, except that he believes "the egg 

 of Syngamus within the perfect worm just arrived at 

 maturity does not contain a developed embryo," whereas 

 Megnin found '' embryos quite perfect and living in eggs 

 not yet freed from the decomposing bodies of female 

 Syngami attached to the tracheal mucous of pheasants 

 that' had died of gapes." 



The discovery of the distribution of these parasites 

 through the instrumentality of earthworms, which are un- 

 doubtedly a favourite food of all young game birds, as 

 well as of domestic fowls, is especially interesting to 

 game preservers, and the theory is strongly supported by 

 their experience. 



First, if, as Dr. Megnin believed, the eggs could be 

 hatched only in water, a gamekeeper could have counted 

 upon reducing to a minimum the risk to his artificially- 

 reared birds by deprhing them of water and feeding 

 them upon food carefully moistened with pure spring 

 water only, or more conveniently, upon avater that had 

 been first boiled. Many have followed this rule habi- 

 tually and with good results, but certainly without se- 

 curing any immunity from occasional outbreaks of the 

 " gapes disease." Secondly, all who have had any exper- 

 ience in rearing pheasants or paitridges, or have observed 

 the growth and health of broods of the young of these 

 birds in a wild state, must have noticed that very dry 

 summers are much more favourable to the maturing of 

 full broods and coveys than those in which a greater 

 degree of moisture prevails, but if after very dry weather 

 copious showers or very heavy dews moisten the surface 

 of the ground when the birds have not yet attained their 

 full growth, an outbreak of gapes is almost certain to 

 follow, and is very rapid in its effects. So long as the 

 ground is hard and dry earthworms do not come to the 

 surface, but whenever it becomes sufficiently moistened 

 to permit them to throw up their casts and to reach the 

 surface, all species of birds of which they form a natural 

 or favourite food are eager to seek and to devour them. 

 The birds named by Dr. Walker as those in which 

 Syngamus has been found are, with the single exception 

 of the swift, all worm-eating birds. He does not mention 

 on what authority the swift is included in the list, but it is 

 difficult) to understand, if water is to be regarded as the 

 only medium of conveyance for this parasitic disease, 

 why many other birds should not also have been found 

 to be affected by it. We believe Dr. W'alker's discovery 

 has been received in America with some incredulity, but 

 apart from the careful observations and experiments on 

 which he relies, the accuracy of which there seems to be 



