How a parasite with the reproductive potential 
of Heterakis could have survived to be a con- 
temporary of man and his domestic birds 
seems not to have distributed parasitologists 
for several decades, probably because a plau- 
sible life cycle could draw that satisfied the 
requirements of transmission under experi- 
mental conditions and might conceivably be 
adequate under the crowded conditions em- 
ployed in modern poultry rearing (24). There 
were plenty of inconsistencies or evidences of 
that intriguing revelation we so often await: 
"There's something about this I haven't told 
you yet," 
Then came a discovery. The ubiquitous 
earthworm, long suspect, was found to be in- 
volved in a very important way (25). The 
Heterakis eggs that it swallows during the 
process of feeding are not destroyed nor do 
they usually pass uneventfully through the 
worm to repose in its castings. They hatch, 
liberating the larvae that then migrate to and 
lodge in various places, such as tissues or 
coelomic cavities, of the earthworm and sur- 
vive for weeks, months, perhaps even longer. 
They escape the harsh action of dehydration, 
irradiation, extremes of temperature, and at- 
tack by predators. The earthworm protects 
them and concentrates them until many 
hundreds may sometimes be present in one 
large Lumbricus, and it provides the all- 
important motive for their ingestion by the 
bird (26). Several other invertebrates may do 
all or some of these things (27, 28, 29). So 
far as we know, none does it so frequently 
or so well as do our friends the earthworms. 
What measures of biological control we may 
take against the histomonad is now unclear, 
To attack only the histomonad requires that 
our attack be directed at stages within the body 
of the bird. This suggests immunological 
methods or, perhaps, the introduction of an- 
tagonistic organisms, a device that occurs 
even in this instance in nature (30, but that is 
difficult to control. Both approaches are being 
studied, but at this time the grower must still 
rely on the use of drugs if circumstances per- 
mit, 
We might attempt elimination of the cecai 
worm, parasite of little economic importance 
apart from its role as a vector. To date, 
chemical control, although only partially satis- 
factory (31, 32), would probably have to be em- 
ployed, along with management methods, to 
achieve the complete, temporary elimination 
of cecal worms, 
Earthworms can be excluded from small 
poultry yards temporarily by various devices 
(33). No one would seriously suggest their 
eradication because of their important role 
in nature. I suspect that any earnest attempt to 
do so on a large scale would touch off a 
holocaust, beside which the tumult that sur- 
rounded "Silent Spring'' would seem but as 
the gentle murmur of the leaves upon a 
summer's night. 
I hope I have not conveyed the impression 
that those of us who believe in the merits of 
biological control as a means of combating 
parasitism are defending a hopeless cause. I 
must admit, however, that we made a tardy 
start. In this respect, we are like the small 
boy being questioned by an adult passing 
nearby what the score was in their sandlot 
game of baseball. 
"Sixty-seven to nothing, their favor,'' he 
gasped between fielding efforts. ''You're getting 
beat pretty badly, aren't you?" the sympathetic 
onlooker queried, To which the lad replied, 
"Naw, we hain't had our bats yet,"' 
REFERENCES AND NOTES 
(1) L, P, Pellerdy, Catalogue of Eimeriidea (Proto- 
zoa; Sporozoa), (Hungarian Acad, Sci,, Budapest, 
1963.) 
(2) E, E, Lund, Histomonas wenrichi n, sp, (Masti- 
gophora: Mastigamoebidae), a Nonpathogenic 
Parasite of Gallinaceous Birds, Jour, Proto- 
zool, 10, 401(1963), 
(3) One product, 2-amino-S-nitrothiazole, became 
available to turkey growers in 1950 and the 
other, 4-nitro-phenylarsonic acid, was first of- 
fered for sale in April 1951, 
115 
(4) Considered in these calculations are the parasites 
enumerated in W, W, Becklund's ‘'Revised 
Check List of Internal and External Parasites 
of Domestic Animals in the United States and 
Possessions and in Canada,"' Amer, Jour, Vet. 
Res, 25, 1380 (1964), 
(S) P. C, C, Garnham, A, E, Pierce, and I, Roitt, 
Immunity to Protozoa (1963), 
(6) F,G,Tromba, Immunology of Nematode Diseases, 
Jour, Parasitol, 48, 839 (1962), 
