Two centuries ago there were more buffalo than cattle in the United States. Even though millions of cattle are killed for beef consumption each year, the cattle population continues to grow while the buffalo are virtually extinct. Why?

Three reasons: Indians, trains and buffalo hides.

Explanation:

The buffalo came close to extinction in the late eighteen hundreds when their number fell down to only a few hundred. The settling Americans needed to get rid of the Indians and of their primary food source, the buffalo. So they eradicated most of them. Another reason was that the buffalo posed a dangerous threat to the new trains that had tracks running across the country. Without the buffalo roaming around the trains would be more efficient and in less danger. The buffalo hides were used for making robes and rugs. Unlike the buffalo, cattle is being mated and cared for.

white blood cells or wbc s are mainly 2 types-

1.agranulocytes

2.granulocytes

the monocytes or macrophages of agranulocytes , dendritic cells which are accessory leucocytes, and b cells which is one type of lymphocytes   identify the antigens present on the pathogen's surface. these three cells are called antigen presenting cells(apc) which are phagocytes and destroy the antigens by secreting antitoxins. besides this leukocyte is always plays vital role in the immunity of the body.