Images Dated 18th June 2003

Technician with bacterial cultures in petri dishes

MODEL RELEASED. Bacterial cultures. Masked techni- cian holding two petri dishes containing bacterial cultures in gloved hands. The petri dishes are filled with different coloured agar nutrient media on which bacteria grow. Lines of bacteria can be seen growing on the dishes where they were streaked. This involves running a platinum wire loop that has been placed in contact with a bacterial culture over the agar. By heating the loop, each successive set of streaked lines leaves fewer bacteria, until round colonies form around single bacteria. This technique is used to isolate particular strains of bacteria, which may then be incubated and grown in pure form

© TEK IMAGE/SCIENCE PHOTO LIBRARY

Blood typing

Blood group test showing reactions between blood types (down right) and their antibodies (across top). There are four human blood types: A, B, AB and O. Type A blood has type A antigens on its blood cells and anti-B antibodies in its serum. Type B blood is the reverse. Mixing type A blood with anti-A antibodies leads to an agglutination reaction, the result of which is seen as dense red dots. AB blood has both A and B antigens on its cells, but no antibodies. Type O blood has both antigens and no antibodies. Anti-D is an antibody used to test for Rhesus antigens, and it reacts with Rhesus positive blood. Typing is necessary to prevent reactions during blood transfusions

© Tek Image/Science Photo Library