Cell chemistry and the contents of the nucleus
Kossel examined the chemical structure of cells through investigations of cells from the glands and blood of birds, gametes of small animals, eggs and other biological products such as milk. He hoped to find out which chemical processes were fundamental to life, and chose to study the nucleus, which is common to both animal and plant cells. He was the first to describe the chemical structure and properties of nucleic acids, and to discuss the structure of proteins present in the nucleus. This work formed the foundations of later work to discover the purpose and structure of DNA.