From the time that western civilization established itself on the North American continent until very recent years, little thought was given to the diseases, or other forms of loss, in game. In the process of bringing civilization and the incidental domestic arts and trades to the United States it appears to have been the policy to establish domestic farm stock on the land just as abundantly as the carrying capacity of land would tolerate. And judged by the low quality of many of our present farm animals, it is evident that in many cases the land was, and is now, overstocked and undermanaged. In traveling over this country one is impressed by the lack of uniformity, imperfect physical development, and poor state of nutrition of much of the domestic livestock. It would appear that the wild animals unhampered by fencing and other restraint such as controlled mating, feed selection, and enforced habitat in contaminated or polluted environment, have a better chance for perfect growth and complete development to a size and proportion normal for those species.

While all of the factors mentioned produce a definitely deleterious result on the welfare of animal life, that of contaminated or polluted environment is by no means the least. The stunting action of disease on the growth of the young is too well known to admit of controversy. The impairment of function of vital organs due to minute cellular changes resulting from sub-acute or chronic infections prevents normal growth. Through centuries of enforced survival in densely congested pastures, pens, and stables, a certain degree of acquired resistance to many diseases has been built up in farm stock. If it were not so, very few barnyard animals would ever survive the conditions generally seen in our agricultural districts. Manure heaps, quantities of partly spoiled feed, and decaying masses of vegetation and refuse have come to be regarded as a natural part of the barnyard scene.