Initially, the procedure for measuring the viability of the cells did not include an MTT assay, but instead a cell count. Photographs were taken of the centers of 24 well plates and the number of cells in each photograph was counted and used to determine the viability of each culture. This method presented two major problems:

1. The wells in the 24 well plate were slightly convex and cells would collect on the sides, instead of being equally spread out, creating a false representation of the cells in each well.
 

2. The field of view was too small which meant that getting a picture that would accurately represent the whole well was highly unlikely as cells are not equally spaced apart.

          It was partly these two errors that led me to repeat the experiment, except this time, perform an MTT assay on the wells. Performing an MTT assay eliminated both the problems mentioned above. With my current procedure, some possible errors were:

1. Bacterial or Pathogenic Agents - It is possible that bacteria could have invaded the cell lines and caused cell death. Since the plates contain only cancerous cell lines, the immune system that normally would have protected them in a human body, are not present to fend off any bacteria.
 
2. Accuracy of Instruments - Although the instruments used for measuring quantities of reagents are considered very accurate, there is always the likelihood of measuring errors, especially when dealing with extremely small volumes of substances. An error when dealing with such small quantities of substances, would have a major impact on the final results.