(4) The yield is also quite variable, this class of products being especially influenced by seasonal conditions and particularly subject to insect attacks and fungous diseases. Since large capital is invested in labor, the horticulturist may be involved in financial ruin through causes which he is unable to control. (5) The labor question, in certain forms of horticulture more than in others, involves difficulties, among which is need of large quantities of cheap labor for short periods of time. CHAPTER XV REASONS FOR ANIMAL HUSBANDRY Animal products in the United States nearly equal in value those of all other farm products. Those soil supplies which constitute the food of domestic animals are not implied. Practically every farm in the United States keeps domestic animals, either for their labor or their products, and nearly every household in both city and country keeps one or more animals for companionship. The domestication of animals has been a prime factor in the civilization of the human race by furnishing man with motive force by which he has been able to increase his productive power; by giving him a larger, better and more regular food supply; and by furnishing the materials for clothing, making it possible for him to inhabit temperate and even arctic climates. Animals have not been less important in advancing the spiritual welfare of the human race, by inculcating habits of regularity and kindliness, which the care of domestic animals imposes. INCREASE IN ANIMAL PRODUCTION