def _create_virus(self, virus_number, row_number):
virus = Virus(self)
virus_width, virus_height = virus.rect.size
virus.x = virus_width + 2 * virus_width * virus_number
virus.rect.x = virus.x
virus.rect.y = virus.rect.height + 2 * virus.rect.height * row_number
self.virus.add(virus)
