rill' inaiiiirc is contiiU'd witliiii wmnli'ii hoxi's oitlii'r :ili<ivi' (ir 

 lielow Kroiiiul — all except the o\iter layer of It iiielie.s heroines 

 hot enough to destroy the panisites, while if the womleii 

 lioxes are doiihle walled with sawdust lietweeii, all are killed 

 ill a week. Kxperiiiieiits with artitieial heat, have shown 

 that steam, at l."i lbs. pressure, destroyed in itO luiimtes all 

 e^Ks and larvae in a special niaiiiire box. 



While these data indieate that iiiainire can In' I'lVcctively 

 sterilized, the iiicthods with the exception of the first, have 

 the disadvantage of leipiiriiiii special a|)paratus. This en 

 tails expense and limits their application to well eciiiiiiped 

 stables. However, a compact manure pile, which has the 

 outer (> inches turned in every .'> days or so, will iiiHloiiliteilly 

 kill a very high percentage of the eggs and larvae. 



3. Drying. This is a method which is only occasionally 

 possible and the drying of large (piantities of manure is 

 l>ractically confined to countries with a hot, dry climate wlu're 

 dried dung is used for fuel, or where its value is secondary 

 to military conditions and it may be spread out in the hot sun. 

 Ill the latter case, however, imincdiate daily <lrying is essen 

 tial as only the eggs and jire infective stages are easily 

 destroyed by this method. Drying is of some value also 

 in destroying larvae on bare ground. Iturning of manure is 

 the logical extension of drving it, but this is seldciru i>raiti 

 cable. 



In a rather dilTerent way this method has been used to 

 combat the lung and intestinal nematodes of silver foxes in 

 Canada. There the animals are raised on floorboards which 

 are easily kept dry by being roofed. This inhibits develop- 

 ment of the eggs and larvae of the worms so effectively 

 that it is now almost routine practice. 



In the open, short grass assists drying and is frciiuentl.v of 

 value ill reducing the infectivity of p.'istures, as of course, is 

 drainage. Very wet iiasturos, however, are not suitable environ- 

 ments for the development of most nematodes (except Did ylo- 

 raiiliix of horses, sheeji and oxen). Damp pastures are more 

 generally favourable for parasitism and every effort should be 

 made to render them unsuitable for the development of eggs 

 into larvae. 



4. Chemical Tre:atmext. Comparatively little has been 

 done to find chemical methods of destroying the free-living 

 stages of parasites. It is a problem which presents many diffi- 

 culties, probably the greatest of which is the faet that the eggs 

 and larvae are always in close contact with faeces, soil or grass, 

 and many chemicals which might be used, are iiartially or com- 

 jiletely counteracted by contact with organic matter. Never- 

 theless, chemical control of all the free-living stages does ap- 

 pear to have considerable practical possibilities. 



It offers the opportunity of using the faecal material as 

 manure and even of enriching the manurial value and it does 

 not necessitate special equipment. 



The method has been sporadically used with a certain limited 

 success in some human hookworm areas, the chemicals employed 

 being kainit, lime and some nitrogenous fertilizers such as 

 nitrate of soda, sulphate of ammonia, and calcium cyanamide. 



The addition of a chemical to faeces containing nematode 

 eggs, may have varied effects on the eggs and larvae depend- 

 ing not only on the nature but also on the quantity of chemical. 



1. It may increase the percentage of larvae which reach the 

 infective stage and which continue to survive. Even in small 

 cultures of fresh horse faeces in sterilized containers, fungi 

 parasitic on nematodes have occasionally become established 

 very rapidly and in a short time have destroyed all the larvae. 

 The evidence suggests that some chemicals may destroy or 

 retard the growth of these fungi without harming the larvae; 

 flowers of sulphur is an example. Other evidence suggests 

 that some chemicals, which are lethal to eggs or larvae when 

 mixed with faeces in a certain i)roportion may, in a lesser 

 proportion, be lethal to the fungi without harming the larvae; 

 it follows that these chemicals may, if used too s])aringly, 

 actually increase rather than decrease the number of larvae 

 which survive. Fungi are more likely to be common in manure 

 pits and similar locations than in cultures and may be of 

 practical importance as a method of natural biological con- 

 trol. It is probable that there are many chemicals of quite 

 different types which possess this danger. A chemical may also 

 decrease putrefaction which may be lethal to larvae. 



2. It may have no effect at all on the eggs or larvae. The 

 majority of the chemicals which can be added to faeces without 

 afTecting the eggs or larvae, are those which are most inert; 

 exam])lcs are ferrous sulphide, ferric oxide, ground limestone, 

 rock phosphate, basic slag, derris root, white hellebore, and 

 pyrethrum powders. 



3. It may allow larvae to reach the infective stage but 

 cause many to exsheath. Some chemicals cause larvae to ex- 

 sheath without necessarily causing their immediate death, al- 

 though most of these chemicals are lethal in higher propor- 



tions. I,ap;ige has shown that the factors which are impor- 

 tant in causing I'xshcathment when free of faeces, include age 

 of the larvae and |ill of I heir environment, and that chlorine 

 and sulphides make the sheath more permeable. Iji the pres- 

 ence' of faeces, some chloriib'S and sulphates, sodium and potas- 

 sium hydroxide and potassiuui peruiang.-inate occasionally 

 cause exsheathment. Tln'se cliemicals, in slightly greater pro- 

 portions, gener.'illy cause the death of larvae. 



4. It may allow many l.nrvae to reach the infective stage 

 but subse(iuently cause their death. Many chemicals mixed with 

 faeces in certain proportions, allow a considerable number of 

 the eggs to hatch and the larvae to reach the infective stage 

 and then kill them comparatively rapidly. The most ontstand 

 ing exami>les so far noted with this property are (piicklime, 

 (in qu:uitities too small to I'.'iiise death through tin' heat of the 

 clieiuical reaction), cupric, ferric and ferrous sulphates, zinc, 

 cupric nitrate, sodium fluosilicate, and oxyquinoline sulphate. 

 Wlicn ajiplied to fresh faeces, in some cases only a third of 

 the quantity of chemical may be required to cause delayed 

 deiith compared with the (luantity required to cause death 

 ln'fore the infective stage is reached. Numerous other chemi- 

 cals (but to a lesser extent) have the characteristic of causing 

 dcl.-iyed death under certain conditions; examples arc nicotine 

 suliiliate, trisodium phosphate, sulphate and chloride of man- 

 gaiu'se. so<liuin and magnesium borates, strong cresol, phenol, 

 anil calcium liypt)chIoritc. 



."i. It may allow a few larvae to survive. It is probable 

 th.it the thickness of the sheath may be an important factor in 

 lircventing the action of some chemicals on the larvae. If this 

 is so. it would account for the fact that, in spite of careful 

 mixing, a few larvae survive in cultures treated with sufficient 

 (or more than sufficient) chemical to kill most of them. In 

 many cases when a few larvae have survived they have been 

 mainly the larger sclerostome larvae. (In some cases the posi- 

 tion of the eggs, e.g., in the centre of a lump of faeces, may 

 have enabled them to survive.) 



G. It may rapidly kill all the eggs or free-feeding larvae. 

 When a chemical is highly lethal its method of causing death 

 may be of considerable practical importance. Chemicals which 

 are lethal but insoluble — they are not common — and which kill 

 by contact would be difficult to use in practice, because many 

 larvae would escape by remaining away from the chemical, 

 e.g. inside a lump of faeces. These chemicals would, there- 

 fore, be especially useless in dry conditions. Applied dry, 

 chemicals which are deliquescent have more prospect of being 

 of practical value, for the moisture which they attract may 

 also attract the larvae. With solutions it is much easier to 

 obtain effective contact with eggs or larvae scattered through- 

 out the manure, especially if the chemical is sufficiently lethal 

 to be effective when applied as a very weak solution. With 

 very lethal chemicals such as iodine salts, it has been found 

 that very considerably less chemical is necessary to produce 

 sterilization with a very weak rathei' than with a very strong 

 solution. In extreme cases a chemical applied as a 1:2 solu- 

 tion may require from 20 to even 50 times the amount neces- 

 sary when applied as a 1:300 or a 1:1,000 solution. 



Some chemicals — including some which are very effective 

 (such as chloropicrin, calcium cyanide, naphthalene, Ortho- and 

 Para-dichlorbenzene) — can be used as gases. Application of 

 this class of sterilizing agent should have many practical 

 advantages, provided that a suitable container is available 

 and that the faeces are not packed too tightly for the gases to 

 permeate them, but results suggest it is possible for a small 

 percentage of eggs or larvae to avoid gases, again probably 

 when they are in the centre of a lump of faeces. However, 

 whether this class of chemical is applied as a solid or fluid, 

 it is probable that the chemical will distribute itself effectively 

 through the faeces. Unfortunately, some of the most effective 

 gases are dangerous or at best, most unpleasant, to man him- 

 self. 



Apart from the efifectiveness of a chemical and ease with 

 which it can be applied, the practicability of its use depends 

 largely on its cost. When sufficient urine is available it has 

 practically all the possible advantages. The next most prac- 

 tical group of agents is the artificial fertilizers, since if care is 

 taken to avoid loss of nitrogen, part or all of their cost may 

 be recovered in increased manurial value. 



Occasionally it may be possible to use a chemical which is 

 not only lethal to nematode larvae, but also to other pests, such 

 as fly larvae; if this can be done the advantages are obvious. 

 Unfortunately, it by no means follows that because a chemi- 

 cal is lethal to fly larvae, it also kills nematode larvae. For 

 example, hellebore, borax, aniline and pyridine have all been 

 shown to be effective in fly control. Hellebore, however, is 

 not lethal to sclerostome larvae, while borax has to be used in 

 larger quantities than for fly control and in greater quantities 

 than are jiracticable if the faeces are to be used as fertilizer 

 (because of the toxicity of an excess of borax to plants). Ani- 



303 



