He use of the isotope 32p as a tracer element in the study of invasion and lysis of bacteria by viruses has shown that

The use of the isotope 32P as a tracer element in the study of invasion and lysis of bacteria by viruses has shown that bacteriophage protein enters the bacteria.

Phosphorus-32 is a radioactive isotope of phosphorus, such that the nucleus of phosphorous-32 contains 15 protons and 17 neutrons, one more neutron than the most common isotope of phosphorous, phosphorous-31.